Doesn't irritate me at all. I actually have a couple of cousins who are married up in age who don't have kids and posts about their pets as "their children" on facebook and that does irritate me as they aren't children and I keep my mouth shut LOL
It also irritates me when a vet tech calls me "daddy" when at the vets and I responded to one in a not so nice fashion that I didn't screw a dog to get this animal.
Fact is, dog or a cat is an animal, not a human being IMO.
That said, if I assume the responsibility to take in a animal as a "pet", I will still treat that pet like a part of the family in that it's my responsibility to care for that animal and provide it medical treatment when necessary.
How many people let their "pets" run free, not even thinking about spaying or neutering their pets and contribute to the amount of unwanted "domesticated pets" in the United States? One of my oldest dogs is a blue tick hound my one son found with my father on our property while practicing to hit golf balls. Reality is he most likely wouldn't survive even in one of our winters in NC at his age now. However, he became my responsibility when we decided to "bring him in" years ago. Sorry, it makes no sense to me to take in a pet and either let it roam free without any supervision if not in a fenced in area or give it some shelter from the elements.
I could raise animals for slaughter for food but don't. If I did, I would still try my best to raise them humanely as possible and then give thanks for their life so that we could eat.
Hopefully you understand my view point a little better.