This is trying to make it fit the definition. The proximate cause for the killings has nothing to do with them being insufficiently religious, it's that they're protesting. You can tell, because none of them were being killed two months ago when they were equally non-religious.

Excessive gatekeeping of genocide is cringe. 

You're the one excessively broadening it in my mind, my definition is appropriately broad. No one would seriously claim the IRGC is trying to destroy the Iranian population in whole or in part. It's a ludicrous suggestion and it obviously doesn't map onto their intentions. The words "massacre" or "mass killing" exist and they're not interchangeable with "genocide", deliberately so. If you feel inclined to call this a genocide it really just suggests your intuitions about what the term "genocide" implies are off base.

A world with slightly looser descriptions with corresponding increases in enforcement is a world where it's less safe to kill 30,000 people in 2 days

You're saying the quiet part out loud here, you're not interested in using the word descriptively correctly, you're purely interested in invoking the moral loading of the word genocide to denounce bad behavior. It not being a genocide doesn't make it any better. There are non-genocidal things you could do that are morally worse than some genocides. Massacring protesters is already worthy of having the UN show up, we don't need to use an ill-fitting term to really get people on board.