There are many hobbies that people engage in, and that do not require much talent or expertise. The main point is that they are fun. In some cases these hobbies may be fun to watch too.
Air guitar is not, in my opinion, of the latter kind.
It may be fun to prance around in the rhythm of a groovy guitar solo and pretend to play an imaginary guitar, but watching it is not very fun. It actually looks ridiculous.
Pretending to play a guitar is not a talent, it does not show anything interesting, and in fact it looks ridiculous and obscene. At least with a real guitar it doesn't look like you are playing with yourself, but without it... It just looks horrible, and I really don't want to watch that.
What's worse, some people take it way too seriously. Heck, there are world championships of air guitar. WTF?
People argue that it's all about the show. Fine, but if you want a dance show, then make it a dance show, not a pretend-guitar-playing show that doesn't require talent, looks ridiculous and, what's worse, obscene.
I don't want to watch that. Give me either a dance show or a real guitar shredding show, not this.