I think the difference between the rugby and the football teams is that the current rugby best XI are underperforming, they are more than good enough to win a 6 Nations yet have not. Since the competition began Ireland have amassed the second highest points total but never won the competition, while teams with less overall points have.
In comparison, the current Irish football squad isnt very strong, however expectations are high and the team has underperformed. No one can tell me that this team man for man is worse than Cyprus for example. What is annoying about this team is that there is potential to be a good team and maybe with a bit of luck qualifying for a major tournament. There seems to be no real reason why the team has consistently performed so bad, (apart from bad management) and the general public now has the view that certain members of the team no longer care about playing for Ireland!!
As for abuse, it is never acceptable. The majority of the players give it their all and that should be respected with their limitations in mind.