I know a lot of people who raise pets in lieu of dating/marriage/kids. Many of them explicitly state so; for others, it is more of a revealed preference.
I love animals, and whenever I visit my family members with pets I enjoy playing with them, same as I enjoy playing with my friend's little kids. But the kind of companionship you get from an animal is inherently different than a human relationship.
For one thing, the animal is by definition inferior; however clever or well-trained a pet is, it ultimately depends on you for food and shelter, and therefore it is in its best interest to charm you. So the relationship is necessarily transactional in a way that human relationships aren't. I'm not saying this makes human–pet relationships unimportant or illegitimate, only that they are limited in the forms they can take.
But I am also not at a place in my life right now where I can assume responsibility for a living thing. I move apartments basically once a year. (I felt sorry even giving away my houseplants at my last move.) And I live alone, so after 10–12 hours a day I spend at work, 8 hours for sleep, 2 hours for exercise and chores .. that's not a lot of love I have left to give to the pet.
One day, I would like to have a cat, preferably of the chubby, hardy sort. I think that Dot and Zero would be nice names for it.