Eh, British politicians have rewarded political violence and ignored constitutional reformers for the best part of 150 years in Ireland.
Political violence works - that is the message of recent Irish-British history.
Of course, political violence also strengthens the resolve of those who are subject to the violence - but that too can play into the hands of extremists.
The more I think about it, the more confused I am at your post. Irish-British history is littered with violence. You don't think British rule was agreed over tea and buns do you?
It's a fairly depressing reality - those with the capability and the will to inflict violence often get what they want.
I also think you are coming at this from the wrong angle.
Paramilitaries are not concerned that their violence alienates the other side. They aren't really interested in what the other side wants, hence the ease with which they are willing to kill the other side.