First of all, just like in any other religion, people are people, first and foremost. Some Pagans probably love roller coasters and some like Hello Kitty, but that doesn't mean all of them do. Secondly, it's very important that you understand (a) not all Pagans follow the rule of "Harm None" and (b) even among those who do follow it, there are varying interpretations.
For many Pagans, equally as important as the idea of caring about animals is the concept of responsible wildlife management. The fact is, in some areas, wild animals such as whitetail deer, antelope, and others have reached the status of nuisance animal. In the state of Ohio alone, in 2007, there were nearly 700,000 whitetails roaming around. Some are hit by cars, others die when the amount of animals in an area outweighs the available resources, and still more are plagued by disease caused by overpopulation. For many hunters, Pagan or not, eliminating some of these animals is seen as an act of mercy and of responsible wildlife management. Not only that, any responsible hunter does so fairly - no shooting at wolves from helicopters, or unethical practices like that.
How do you think our ancient Pagan ancestors got their food? They hunted and fished and trapped, and caught it. Most of the Pagans in centuries gone by were not vegetarians. They were people of the land, who lived responsibly and caught what they could eat. What they didn't need, they left alone, allowing it to scamper away and go on to create life for the next season. Most ancient cultures had deities that personified the hunt. In parts of Britain, Herne (an aspect of Cernunnos) symbolized the wild hunt, and was depicted wearing the antlers of a great stag, carrying a bow and horn. In Greek mythology, Artemis is not only a goddess of the hunt, but also a protector of animals.
For a lot of modern Pagans, hunting is a way to get back to the natural world as our ancestors did, to provide healthy food for our family, and to pay tribute to those who survived hard times in centuries gone by. In some traditions, the hunt is still ritualized, and the deer or other animal is honored as sacred following the kill. Even the consumption of the animal is celebrated.
Hunting is one of those issues that there are clearly dividing lines on in the Pagan community. However, much like eating meat, it's one of those things that you don't have to do if you don't want to... but don't be surprised if people get irritated when you try to lecture at them about it.