Goku never seen Zeno's erasing things before. It's logical that he tried to not risk anything and run away. Especially that Mai was around them and nobody wanted her to get hurt. And Zamasu at that point became the world itself so it equals.
Goku's a fighter, he should obviously have the intuition to know that something dangerous is coming, even when he can't sense it (such as the Beerus fight). We also know that he's great at judging people's intentions (such as his first meeting with Trunks or Broly). There's little reason to not trust Goku's assessment of the situation, especially from someone as to the point as Zeno.
And it makes no real sense for the narrative intention of the scene to be that
"Nobody will actually get hurt, but just to be sure!" rather than
"Zeno is a powerful God that doesn't care who gets hurt"
Likewise, Shin and Gowasu are there too, and agree with Goku that everyone, including them, should leave. Plus, stuff that clearly aren't Zamasu, like the planet they're standing on, got destroyed too.
So that point doesn't really hold up to me.
[Edit:
I also remembered the Manga, where they make it pretty clear that they were gonna die to the blast too, 100%]
And the point about it being a technique with more doesn't really change anything, my man.
The energy still comes from Zeno in the first place. Before it can be used on someone else, it has to start from inside him amyways.
(I'm also pretty sure Hakai can be used from a distance. Doesn't Sindri erase a city while in the air?)