I would much rather have relevant advertising. I don't visit forums where there are different classes of members, and I'm not going to start doing so.
We invest our money in companies, so they should be the ones investing in the community that is buying stuff from them.
And fees do not "ensure longevity of a stable and friendly community" They pay for the things such as hosting and bandwidth that any site, regardless of whether they charge subscriptions, has to pay.