To say that if you use this special pronunciation option you “fail to speak properly” is lunacy. The truth is the opposite: you fail to speak the normal style of Standard English properly if you don’t use [gənə]. Saying “I am not going to put up with it” with every vowel and consonant pronounced individually in its stressed form makes you sound like an extraterrestial (“Do. Not. Fear. Us. We. Will. Not. Harm. You”).
I’d like to raise both of my middle fingers to him and anyone who thinks profanity is somehow more harmful to our children than images of violence and misogyny.