I tend to not worry much about shrimp welfare, I think it's fine/reasonable to use insecticide (etc), but I also wouldn't make a habit of torturing ants or something
The last thing any person would want to discover, I hope, is that they really enjoy torturing other living creatures. At the point where you've determined someone feels that way, the best you can probably do is try to set them straight and hope they understand why it's not appropriate behavior.
It is tricky to evaluate in a broader context though - for example dolphins have been observed engaging in behavior that resembles torturing other animals for fun. So maybe this sort of thing is actually just ingrained in the nature of all near-sentient and sentient beings. I'd prefer if it weren't.