"...Minister Reid. "The seal herd is in excess of five million, and as the herd continues to enjoy a population explosion,..."
2003 Newfoundland Government statement
This amount - 5 million seems to me like the seal herd is not in danger of extinction. I personally feel that humans have as much right to cull other animal populations as any other creature. Our responsibility is to do it carefully enough as to not harm the the populations of animals such that it causes underpopulation of that animal or overpopulation of another creature.
If this hunt is being regulated, restricted to a certain time period, and certain maximum number harvested it is no different than deer hunting, or other game hunting in the U.S.
I know some deer hunters who are not interested in the meat very much. Some keep the fur, look for big racks and mount the heads. What is the difference between doing that and wearing the fur? Especially when you consider that the fur makes a much warmer coat and is even sturdier than wearing artifically produced materials which do are not biodegradable, rip and come apart more quickly and are thrown away almost yearly by some people. If you're truely concerned about the environment then you have to consider the entire cycle of each item you use.