Um DOTA 2 has 2 casual modes.
Ability draft & single draft.
Also the Thicker Skin argument I will agree doesn't work in MOBA games. I've fond growing a far more spiky skin helps. I play support generally (AKA the role who gets least praise and most crapped on). My attitude has gone from thick skin and taking it to "Oh no you did not just throw a hissy fit at me" I've found it works far better with most allies that the moment I start getting shit, I throw it back ten times harder at them.
The general way it goes is
idiot "OMG report noob support no courier GG noob"
Me "I bought the wards"
Idiot "you're a support you buy the courier"
Me "get the other support to do it"
Idiot "There is no other support"
Me "Not my damn problem is it then"
Idiot "Yes you support you buy courier"
Me "No Me a support, me the support that buys wards"
Idiot "Buy courier idiot noobs support"
Me "Oh I'm the idiot am I, because out of the 4 of you, you couldn't figure it out to pick a second support and all wanted to carry"
Idiot "Reported Noob support, we only need 1 support"
Me "this isn't LOL you Noob Dota 2 standard is 2 supports, it's not my problem the 4 of you all picked selfish heavy farm dependent carries"
It generally deals with them well. I someone else is criticising others play I tell them to shut up and focus on their own play as then they'd not suck so much ass.
Or if someone really gets on my nerves I've drop all my support items and tell them to do the job and just go off to the jungle and farm. Sure we'll lose but sometimes annoying particularly vile players is worth the loss to force them to learn.