If someone's spent their hard earned cash to go to an away game, they're more than entitled to voice their opinions whether that be before, during or after the game, inside the stadium or not. A dispute happened next to us at the Lithuania game, where a lad shouted something negative and it was met by a guy shouting back at him to "shut the f*** up and get behind the team" (which in my opinion was out of order)
I'm a Dons fan, so I know what going through a living hell for 90 minutes can really feel like and if people want to voice their opinions, then so be it. They've paid a lot of money for their ticket, travel, accommodation etc, so they're allowed to feel a bit aggrieved when the players in front of them are going through the motions against an Eastern European minnow.