"Well, first off, you'll have to stop READING LJ, too, because ad rates come from pageviews and clickthroughs, not posts per day.
Also, withholding content only works if they WANT your content. This strike is like a gay sex strike to protest for gay marriage.
SUP is hiding the fact that people post about fandom, fantasy, homosexuality, etc, on Livejournal. Don't you think it would make their day if people ACTUALLY DIDN'T post about those things? If we all just went away, they would be HAPPY.
Fandom is not a big enough section of Livejournal content providers for them to be hurt by this. They're just not. I know the number of members in fandom_counts seems like a large number, but the thing about numbers is what makes a number big is what you're counting. 50 is a lot of elephants but not a lot of cents. 35,000 fandom_counts members out of 13 million LJ members is .0003 percent.
I know in our usual LJ enclaves it seems like "everyone" is pissed off, but when these posts come up in news, the VAST majority of responses are "lol sing moar pirate songs nerds." People who care about this are outnumbered there 10 to 1, and that's just the people who care enough to read news. There's a vast uncaring bulk of LJ users who pay no attention to the mechanics--they just want to know who hooked up with who at Jason's party.
A fandom strike will not even be a blip on SUP's radar, and if they do notice, they will be pleased. An unpopular vocal minority has NOTHING to gain from silence.
If you want to protest the censoring of the popular interests list, post LOTS of fanfic and gay porn and stuff about mental illness and faeries to up the odds of that coming up when someone clicks "show me a random post" and gets introduced to what LJ is all about."