I suspect a lot of people do, but how strong it is varies. I would take a look before, with an eye out for crankish or biased tendencies. Of course by the time I got here I knew this was legit.
A possible way to defuse this would be to add a second tagline that motivates understanding rationality for the purposes of building it. Then the agenda becomes clearer: yes, it really is rationality, in itself, for a specific purpose.
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.