Future isn't the first rapper to rap about Xanax and I'm sure he won't be the last. Shit rappers been rappin' about drugs for the longest (primarily weed and coke). I don't know why Vic Mensa is tryna make Future seem like the poster child or advocate for Xanax.
These are just a few examples. I'm sure there are plenty more though.
Vic Mensa is actually pretty dope. (Listen to Autobiography).
I don’t really get him trying to save heads by condemning Futurethough.
And the only explanation I can come up with for Future being as popular as he is (among siccness members as well) is that all his fans have never listened to his music sober.