You might think that market research is unnecessary since you aren't trying to make money from your mailing list. Wrong! While you might not be looking for a profit, you are going to invest a lot of time and energy into the list, so you may as well make sure it's going to be worth it.
The two most important things to check are firstly, is there a need for the list, and secondly, does another list or forum exist already? Find out the answers to these by asking in related fora including other mailing lists, newsgroups, web-based bulletin boards, IRC or other chat facilities, etc. Don't just ask "do you think it's a good idea?" but specifically ask people if they would subscribe to such a list if it existed.
If it appears that there are people interested in your list (a dozen positive responses should be sufficient), and if there is no other list already doing exactly the same thing, then by all means go ahead and start your list.
If you do not get any expressions of interest, you will probably find yourself on a very quiet list, talking to yourself. If you find that there is another list with an identical or similar purpose, join it and read/contribute for a few weeks before you make a final decision either way -- it may be that your list would be differentiated in some important way (geographical focus, noise level, etc), in which case it will probably be worth going ahead anyway.