I'll try to help you understand why (I think) some people feel the sting of the repugnant conclusion (RC), but why I think they are ultimately wrong to do so. I should say that I personally don't find the repugnant conclusion repugnant so what I'm about to say might be completely missing the point. I am slightly stung by the "very repugnant conclusion", but that might be for another time.
In short, I think some people find RC repugnant based on a misunderstanding of what a life "barely worth living" would mean in practice. I think most people imagine such a life to be quite "bad" on the whole, but I think this is a mistake.
Note that the vast majority of people on earth want to continue living. This would include the vast majority of people who live in extreme poverty or who are undergoing horrific abuse. It would also include people who constantly consider suicide to end their pain but never go through with it. In normal parlance we would say these people live "bad" lives. However, we might conclude that these people are living lives worth living if they don't want their life to end / don't choose to end their life. So my guess is people imagine "a life barely worth living" to be a pretty "bad" one. The actual wording of "a life barely worth living" is inherently negative in how it is framed anyway. So RC would amount to a load of people with pretty "bad" lives by intuitive standards, being better than a smaller number of people with absolutely amazing lives. Accepting RC would be like creating another Africa with all it's poverty and hardship instead of creating another Norway with all it's happiness. Or creating loads of people attending daily suicide support groups rather than a smaller number of people living the best lives we can imagine. Most people would find these repugnant things to do and I personally would feel the sting here.
The problem with the above reasoning becomes clear when we think more carefully about "a life barely worth living". Firstly, to state what should be obvious, such a life is worth living by definition. So to be put off by the existence of such lives doesn't really make logical sense, unless you deny the theoretical existence of positive lives in the first place. This doesn't negate people's feeling of repugnance, but I think it should cause them to question it.
Where does this leave us with people attending daily suicide support groups? Well my preferred way forward is to question if these people do in fact have lives worth living, or at least to question if we have any idea on the matter. As is pointed out by Dasgupta (2016), the idea that someone who wants to continue living must be living a life of positive welfare ignores the badness of death. It is certainly possible for someone to be living a life of negative welfare, but be reluctant to end it because the subjective badness of death exceeds the badness of continuing to live. Death is indeed a horrible prospect for most when you consider factors such as religious prohibition, fear of the process of dying, the thought that one would be betraying family and friends, the deep resistance to the idea of taking one’s own life that has been built into us through selection pressure would cause someone even in deep misery to balk, and the revelation of one's misery to others when one wants it to remain undisclosed even after death.
In light of this Dasgupta puts forward the "creation test" as a way to determine the zero-level of wellbeing. What is the worst life that you would willingly create? Dasgupta says that should be the zero level. Most altruists wouldn't create more people living in extreme poverty, or people with constant thoughts of suicide, implying these people probably live negative lives. I personally would only create a life that most of us would say is very good!
I'm not saying Dasgupta's creation test is perfect - I'm undecided on how useful it is. This paper argues that we have no sufficiently clear sense of what a minimally good life is like. If this is indeed true, as the paper argues, the RC loses its probative force because we can not judge lives "barely worth living" as being "bad" as we don't really have a clue.
So to sum up my rather lengthy response, I think that many people who think RC is repugnant assume that "lives barely worth living" are those we would say are "bad" in common parlance which can lead to an understandable feeling of repugnance. I think they are wrong - either "lives barely worth living" are much better than being "bad", in which case RC loses repugnance, or we don't know how good "lives barely worth living" are and RC doesn't even get off the ground at all.