disclaimer: My wife (who snowmobiles too) works at REI.
In my opinion, buying a stove or some back country gear from REI isn't going to jeopardize our riding areas. Boycott them if it makes you feel good, but I doubt you'll effect thier bottom line and send a message. So many companies support environmental causes and much of what REI does is good. My wife is an Outreach Specialist and is responsible for organizing community and volunteer projects on local parks and trails as well as education for people new to outdoor recreation. REI has been sucessful in the outdoor industry, but they aren't an "evil corporate empire". Yes there are lots of "greenies" there, but the same can be said about any outdoor retailer.
I wouldn't be caught dead giving money to the Sierra Club, but I'll still buy from REI (even if my wife didn't work there). They carry high quality gear and stand behind it. You can take anything back for any reason, no questions asked. If they refuse to take something back, ask for their manager. They'll be fired. It is extremely rare to find any outdoor company that is this commited to customer statisfaction. Some people abuse these policies, but it is a culture that creates loyal customers.