This is more sort of an ethical question than anything else.
Ok so the yeerks main arguments are that its unfair for a sentient, intelligent being to be so sensory deprived, which is why they infest other hosts.
Well thats the way they evolved right, so tough luck? But they also evolved the ability to infest other beings, so in actual fact they are just doing what they have evolved to do. This was just limited to the Gedds and thats the way it would have stayed, presumably since the Gedds were cumbersome and incapable of making any kind of technological breakthroughs.
So who's to say what the yeerks are doing is wrong? Would you say humans destroying habitats to provide for themselves is wrong, no because fundamentally its down to survival of the species. Sure humans don't go out of their way to harm other species but if there were ever a situation where we had to eliminate a dozen species entirely to save our own we would do it in the blink of an eye.
While I think its right for humans to fight back and resist the yeerks, I've gotta say they are just looking out for their own species, hell at least they're not killing each other to same scale that we have done.