I don't think it's wrong at all. Especially in a situation where the cat is basicly a stray. It's better it gets done by someone if no one else seems to care, because the more kittens on the street the more ferel cats there will be. Or heaven forbid they end up at the shelter in abundance and are killed.
It's not like you walked into someone's house and kidnapped their pet withought their knowledge. This is important. When we adopted our cat from the animal shelter they insisted we get her fixed because people have such a bad reputation for just dumping kittens that their cats had. My last base we lived at, the area was over run by stray and abused dogs. It was sickening. I'm sure they were breeding pit bulls to fight as well. The animal shelter often had free events to give people free pet things they needed and to discuss spaying and neutering. Unfortunately people still didn't get it.
