You can't really knock selfie-taking unless you knock a whole load of other stuff.
Selfies are just a manifestation if our box-ticking urge. If it's not on Strava it didn't happen, Monroe bagging, twitchers, Eddington number obsessives.
A lot of us do it. We can't just go for a walk or a ride, we have to have a box to tick, we have to get to the top of something or ride a challenge distance or maintain a streak. It's natural, there's nothing wrong with it. At least, there isn't until we start trying to impose our silly rules on others.