Wouldn't dropping the rationality tagline instead convince people even more thoroughly that it's not actually about rationality, but rather something else?
That being said, I agree with those concerns. LW doesn't have an agenda per se (beyond being sponsored by the SIAI), but the LW majority clearly does. While harsh, "a bunch of fringe technophiles" accurately describes a significant, and vocal, fraction of people here.
Nowhere have I seen the dangers of AI more focused on than in LessWrong - as such I don't think LessWrong could be accurately summarized as being particularly technophilic.
Concerning Less Wrong's tagline, consider this plausible reaction of someone looking at LW for the first time:
And here are two real quotes from 2009:
And in reply:
The quoted text speaks for itself really. So therefore I think LW's admins/web designers should seriously consider replacing the rationality tagline with something more savory.