DC used to have ads a long time ago, but the community is too tech savvy to either see them or click them, so there wasn't much money to be made from displaying them, so rather than having them detract from the site, mouser decided to get rid of them.
The only time he thought of bringing them back had nothing to do with raising money to support the site. He wondered if he put Adsense back on the site, would Google spider its content better (we were having a bit of a problem with the Googlebot). At no time was this site ever in jeopardy of traveling down the path you described, if the ads were reintroduced. It also wouldn't have been permanent.
The final decision not to do it was based on the fact it wouldn't have resulted in what we wanted because the site wouldn't be any better spidered by the Googlebot, because content spidering for Adsense is done by the Adsensebot, for a different purpose, with different results, and the results are kept separate from the data that is used by Google's search engine.
The LiveJournal group she described is the end of life, after having it's time in the sun, going through sale, and almost everyone leaving...kind of where Friendfeed is today, and where MySpace will soon be. That doesn't describe DC at all, since we are still growing, not shrinking; and the site has not been sold. DC can not enter that stage as long as mouser is still here and cares about the site.