Correction:
Carryong (sic) ANY GUN with a round chambered and no holster is a very bad idea.
Glock is no different than any other gun, it WILL fire if the trigger is pulled - whether by accident or on purpose, it doesn't care.
This is a weird version of pistolero political correctness
Of course some guns are more dangerous than others to carry Mexican Carry, and a Glock is one of those guns.
I carry a USPc. 99% of the time I carry it cocked and locked in a holster. Sometimes though, due to special circumstances, I'll Mexican Carry it, but DA and safety on.
For example last weekend I was carrying IWB on a 1 hour car ride, and it became uncomfortable at the 4 O'clock position in my bucket seats. Before starting the trip back home, I unholstered it, decocked it to DA and re-engaged the sweep down safety so that it was in DA and locked mode.
Then when I stuck it in my waist band, appendix carry, my thumb was over the hammer so if anything caught the heavy DA trigger, not only was the gun in DA and with safety on, but my thumb blocked any rearward movement of the hammer.
I would never ever ever ever do that with my Glock while it had a loaded chamber, full stop, end of story.