The going price for babies on the Internet is as much as US$15,000, according to this CNN story. Unicef reckons that the international trade in human babies is worth as much as US$25 million a year, with some parents prepared to pay as much as US$20,000 to secure a choice specimen of babyhood.
Puppies can be had for free from your local pound. Even if you want to buy a purebred puppy from a reputable breeder, you'll probably pay no more than a few hundred bucks.
One of the most fun things about choosing a dog is that you get to choose between hundreds of breeds, each with its own physical characteristics and temperament. If you want a baby that's not the exact same breed as you are, the best you can do is crossbreed and make a mongrel in the process.
Similarly, with babies you're stuck with the questionable contents of your own gene pool. Any registered dog breeder can provide you with comprehensive, verifiable information about your puppy's family history. You may be a bitser but your dog doesn't have to be.
Women: you don't have to kiss your youthful figure goodbye just because you need to hear the pitter-patter of tiny feet around your home (extra bonus: you get twice as many tiny feet). You also won't have to endure morning sickness, midnight cravings, post-natal depression or hours of painful labour. You will not visibly lactate every time a dog barks in your neighbourhood, either.
You will never have to change your puppy's nappies. With careful housetraining, an eight-week-old puppy can be taught to go out back in a week. True, they'll never learn to use the toilet, but imagine how easy parenthood would be if human babies could be taught to crawl through a flap in the door and shit in the yard?
You also don't have to buy a puppy the latest clothes, music, or video games. Apart from a little obedience training, there are few educational costs associated with dog ownership. Your puppy will never ask to borrow the keys to your car, and will never call you in the middle of the night to tell you they've wrecked it. A puppy will not insist on playing heavy metal music at an ear-shattering volume in your house, nor spend it's entire adolescence on the telephone while you are expecting an important call.
After a lifetime of gently introducing puppy to progressive ideas and paying for a university education, a puppy will not repay you by joining the Liberal Party and becoming a real-estate agent.
Parents of teenage children will immediately understand the attraction. Just imagine how easily you'd sleep tonight would be if young Jason or Britney had had their gonads removed when they were six months old.
You can also have your puppy microchipped, and force it to wear a collar tag listing its name, address and your phone number, so that it can be immediately returned to you should it stray.
Which, when you think about it, is about the point at which most parents begin to really regret having kids. Even if you grow tired of little Rover, there's no shame in putting him up for adoption after a few years trial run. Children, however, tend to harbour grievances against their parents if they do this.
Chances are, you will outlive your dog. You will get to see it grow from a gangly puppy into a responsible, protective adult, you will nurse it through its senescence and it will pass away loving you as much as it did the day you brought it home. You don't get this kind of closure with kids.
You can also get drunk and take drugs while they're around, forget to feed them every now and again, let them go months at a time without a bath, tie them up in the street while you go shopping, and leave them alone and unsupervised from an early age ... all without attracting the attention of the social services. Dogs won't discuss intimate details of your life with other dogs, and even if they do the other dogs won't be able to tell their humans what a pig you are.
Your dog will never call you names, resent that you don't make as much money as their friends' parents, or put you in a retirement home. Your dog will accept discipline when you give it, and will learn from its mistakes.
Puppies have long memories when it comes to important things, like: it's not OK to go through the garbage, no matter how good it smells; but very short memories for unimportant things like: I was just going through the garbage and that bitch/bastard yelled at me. Human children are the exact reverse.