As an Englishman, the IRA were fairly critical to the political results. They kept the UK government from running roughshod over the Irish political parties.
The IRA proved they were willing to cross critical lines (bombs aimed at large scale civilian damage on English soil etc). They also demonstrated restraint. They often provided warnings ahead of time. They focused on disruption not casualties. The underlying threat was clear however. If you (UK government) escalate too far, it's simple to switch from a bomb aimed at destroying a high street of shops, to one aimed at killing a high street of Christmas shoppers.
The end result was that Irish politics stayed in the public eye, and the government took the safer path of negotiating in good faith. No-one was particularly happy with the results, but no-one was excessively unhappy with them either. Often the best you can hope for.
In short, the credible threat is required to keep all parties honest. Most smart governments will see an escalating trail of protests as part of that. Unfortunately, the current US leadership doesn't seem that smart.
For most governments it's enlightened self interest. Completely screwing over their population for short term gain is akin to cutting off your feet to save money on shoes.