Why did the other deities just sit and watch Beerus seal old kai?

[IntangibleFancy]

If I recall, this happened in a meeting between the GoDs and Kais. With so many people there no one thought to stop Beerus?

[Bruma rabu]

Well do they even know this happened? They might not even know, and even if they did they don't really seem like the type to care. Heck his action might have encouraged the other gods of destruction to do the same, you know? Since their lives are connected, good way to keep their other half from dying.

[theherodjl]

If I recall, this happened in a meeting between the GoDs and Kais. With so many people there no one thought to stop Beerus?

Who would think of trying to stop a Hakaishin? Even if it was 75 million years prior when Beerus was green to his role, anyone worthy of the Hakaishin title will always be stronger than a Kaioshin. Sealing Rou Kaioshin in the sword didn't cause harm anyways, it actually ensured Beerus' own survival at the time. Additionally, Whis would've put an end to any physical conflict, he does also fulfill the role of a mediator.