Of course, I also don’t eat meat eggs or milk, don’t wear leather, and haven’t for over 15 years now. But it didn’t happen all at once, and if I just thought that moving snails out of the way wouldn’t make any difference anyway I probably would have given up there and then. But instead I did a little bit more every once in a while until I’m at the point where I am.
So yes cats kill billions of animals a day for example but that’s only if you let your cat out. Every vet we spoke to said that it’s better to keep cats indoors because they live longer lives, don’t get diseases, don’t get maimed, don’t fight, don’t get hot by cars or even caught and tortured by humans (that’s a thing), don’t get obese from eating at home and at the neighbor’s and as long as you make sure they have toys and windows to look through they don’t mind.
My cat has killed maybe four mice in the 8 years I have her, tops. It’s unfortunate that cats must eat meat to survive but the canned food is pretty much the only meat we buy which is a fraction of what most people consume. That cat was abandoned and we took her in.
In conclusion, yes, focusing on the wrong thing is diminishing your impact. But I’d bet that for most people it’s not choosing between high impact and lower impact actions, but rather between nothing at all and anything at all. In that case I still believe anything at all is better than nothing at all. And doing anything at all might raise your awareness to do more and more on top of it.