This question resonated with me, so I signed up just to answer. The short answer is that one would hope that it shouldn't be a point of no return. But, of course, it depends heavily on your supervisor’s temperament.
I was in a similar situation where I was deeply unhappy with the direction and content of my PhD research and despite my best efforts at raising these concerns I struggled to alter things. This was partly due to having two supervisors with not entirely overlapping areas of expertise. However, my main (on paper) supervisor and I met for a coffee in a neutral location, i.e. off campus and not his office, to discuss things. He was non-judgmental and supportive and, having done a PhD himself (naturally), he understood the situation. I did end up leaving the PhD programme but it was not because I couldn’t discuss things with my supervisor (I’ve since completed my PhD at a different University).
So my suggestion would be definitely do not simply quit, you should feel able to discuss issues with your supervisor. After all (at least in the UK) supervisors are expected to provide some level of pastoral care, as well as directing research. If you'd feel more comforatble suggest a neutral location. Further, I’d reiterate what Dave Clarke said in that I don’t know a single PhD student who, at one time or another, wasn’t fed up with some aspect of their PhD.