There is hubris in thinking you are immune to marketing, and if anything it makes you more vulnerable to it.

Celebrity isn't so easily defined. What if Bruce Schneier, who you could consider a "celebrity" of sorts in the security community, started (subtly) promoting Signal Messenger in his tweets and blog posts. Wouldn't you want to know if he was being paid to do that?

This is essentially what is happening when PewDiePie promoted a video game.