He's not stupid for wanting to be better than Goku in a fight. That is fine, it's just a goal and it's not a stupid goal. Heck, it's more or less the goal of most of the cast. However, since Freeza had a pretty sure way to actually become better than him in a fight that was much better than any other option he had, and he intentionally didn't use it purely out of laziness... now that is being stupid.
A simple miscalculation would be something like not applying enough force for Namek to immediately explode, like Freeza actually did when he was on Namek. That's a miscalculation. Freeza's choice in not training is much more than that.
Freeza replied to the idea of training with an additional Kienzan once it was suggested by Goku after he already lost. Him deciding not to train after receiving an additional power-up and help from another powerful being is staying true to the character. He admitted that he's never "felt a need" to train, so it's more or less just Freeza being Freeza.
Like stated, Freeza had a pretty sure way to beat Goku and be the strongest.
So was his mechanization. That power-up gave him a reason to
ignore the idea of training. Freeza being weaker upon resurrection and knowing that his foe defeated Majin Boo was what convinced him to train. Getting vengeance was something he was thinking about
before he even decided he was going to spend a few months training. It's quite clear that training is not something that just happens to enter his mind.
He intentionally chose to not use that option out of laziness.
This
accurately sums up Freeza in general. You're the one trying to pretend he's infallible.
That's being stupid. And lazy.
Lazy, not stupid. Goku giving Freeza a chance to leave the world is stupid. He even admitted to Trunks that he was stupid for sparing Freeza back on namek. Freeza not training his Golden form is hardly any different than Freeza believing his Mecha powers alone were enough to change the outcome.
Not at all. Freeza attacked Goku on Namek when Goku was letting him go. Do you see me complaining about that? No, because Freeza not being calculating and careful after he had just lost and been humiliated (and while he was still in the heat of battle) is perfectly understandable since he is also pretty arrogant.
Arrogance ties in with him believing his mechanization is enough for him to believe he's the strongest in the universe again. Freeza's never felt the need to train, so he never did. Not stupid--it's just what the character is about.
However, after Freeza was put back together, Freeza was no longer in the heat of battle and he had all the time in the world to reflect and think on what to do. In those circumstances it's no longer understandable for Freeza to not be not even a little bit calculating or careful and not choose the best way to make sure he beats Goku in combat.
Freeza ultimately did the same thing back then that he did in RoF. If he took time to tune-up his Golden form, he wouldn't have lost. Instead, he decides to go to earth without even bothering to see the glaring weaknesses it had. That was the reason why he lost....again.
You can get on Freeza for not training after acquiring his Mecha power-up, but you can also get on Freeza for being too lazy to eliminate his weakness. The similarities between the two? Freeza gained incredible power and immediately wanted to test it out. His mechanization allowed him to believe he had all the power he needed to win, and the same applies to his Golden form. That's the main point. His characterization is fine and in no way different.
"Not well thought out" is how we can describe most of the actions that are stupid. And like I said above, blowing up the Earth would only make sense if he wanted to just kill Goku, not if he wanted to beat him. And he wanted to beat him.
It being stupid is just your opinion, though. Freeza was told he'd only need to regain his stamina and learn some new techniques by the guy who bested him. That alone implies their powers weren't very different. He gets a huge power-up and thinks that, along with King Cold, would be more than enough to handle Goku. Not raising his power to overkill levels isn't stupidity in the slightest.
If that was his only option, it wouldn't be stupid. But he had a much better one. He chose against it out of laziness. That's what makes it stupid.
You're looking at Freeza from a a very black and white standpoint rather than accepting that the character doesn't always make the right decisions. Mecha Freeza was regarded as a "demon of vengeance" upon being rebuilt, so we know for a fact that it was an obsession of his. The additional power-up made the decision to go to earth even easier. That's really all there is to it. Nothing about Freeza being stupid, or his characterization being out of place, which is really just your opinion.
Know what would be out of character? Freeza acquired a huge power-up, the additional help of King Cold, and still feeling a need to train when he already believes he's stronger than Goku.
And he was right. They told Freeza about Vegeta's power level and Freeza figured that it wasn't enough to take them both out at the same time. In fact, Zarbon didn't even need Dodoria, he defeated Vegeta all by himself. And, despite this, Freeza still called the Ginyu force because he still felt it was prudent.
Because he wanted scouters
and wanted them to interrogate Vegeta to find the balls. All of those things could've easily been done by him without calling the Ginyu, but he didn't want to do it. Looks like more laziness for Freeza.
You think I'm fixated on his lack of training but that's not true at all. I know what Freeza wanted: to beat Goku in combat and kill him. The course of action with the greatest chance of success in achieving this goal to Freeza's knowledge is to train for a bit. Yet, he chose not to. That seems stupid, but maybe there's a reason why his choice might be perfectly understandable and not stupid?
Yeah, except declining the option containing "the greatest chance of success" is in no way synonymous with being stupid; especially when there were other options on the table. Also, another thing you're seemingly ignoring is that Freeza wasn't even thinking about training until after he realized he was weaker....and that Goku defeated Boo. Freeza
Let's see, Freeza had previously been portrayed as calculating and careful... and this time around Freeza is not in the heat of battle and he has all the time on the world to think about what to do... So, no, I can see no reason for why it might be understandable. So, yeah, I think it was stupid.
The only big picture here is that Freeza could have ensured that he would beat and kill Goku with a bit of training and become hundreds of times more powerful. The only one stupid enough to be fixated and that refused to see this big picture, even though he knew he could improve by that much with a bit of training, was Freeza.
Misjudgment of the situation makes more sense in this context than stupid. The idea of training was
never on his mind, so to say he was already aware of what he could do with his dormant power is an assumption.
After what happened on Namek, and after what happened on Earth, and after being dead for decades Freeza almost didn't use the best option he had to beat Goku again? How does that make him look any less stupid?
In this instance, I gotta admit that it's really stupid he only considered training after realizing he wasn't as powerful as before. This is pure stupidity. It's almost like he expected Goku to stay the same, but then he admits he expected Goku to be more powerful and says he'll have to just get stronger as well. Weird.
"First I whip it out! Then I thrust it! With great force! Every angle...! It penetrates! Until...! With great strength...! I... ram it in! In the end... We are all satisfied... And you are set free...!" ~Dante~
