> I'm not sure if (or why) this leads to the requirement to have a rational discussion with proponents of abhorrent ideas.
Who decides what is abhorrent? In what sense? Rational, yet undesirable?
> abhorrent ideas should be confronted
This is an entirely different think. A constructive (cooperative), rational discussion is different from an adversarial debate.
> to allow abhorrent ideas to spread
Again, who decides which ideas are to be silenced? And without discussion, in this case.
You are essentially advocating restricting individual choice, by restricting available information; pushing individuals towards the "correct" viewpoint by banning advocacy of any other. The US, in particular, and many other western countries, were founded on opposition to this philosophy.