Ian Paisley

I'm not sure I know enough about Northern Irish history to offer an informed opinion about the late Ian Paisley. 

i) From what I can tell, he was an opportunistic hatemonger who used uncompromising rhetoric in his rise to power, only to backpedal after the fact. He probably succeeded in alienating all sides at one time or another. 

ii) That said, some of his rhetoric, which many people find so outrageous, overblown, and shocking, reflects traditional religious polemic, from Luther, Calvin, and the Westminster Divines. Moreover, it's not as if Catholicism was any more charitable. Take this papal specimen:

http://www.papalencyclicals.net/Leo10/l10exdom.htm

iii) I also suspect that to no small extent, his belligerent pose mirrored the defensive mentality of a politically threatened religious minority (i.e. Protestants). To my knowledge, Catholicism is the majority faith in Ireland at large, but the partition of Ireland made it the minority faith in N. Ireland. So there's that demographic tension. A kind of internal/external border war.  

Up to a point, Protestant insecurity is understandable. They have, or had, reason to fear. Ironically, the Irish Catholicism has been politically weakened, both from outside forces (secularism) and inside forces (the priestly abuse scandal).