Well, I can tell you from experience what I think as the RCIA candidate.
I was confirmed just last year at the age of 19. During RCIA, I threw a legendary fit about the contraception teaching. (Not an immature fit, but like an “ARE YOU SERIOUS” fit.) I know for sure that I will have and most likely will want a career for most of my life, so the idea of lots of kids didn’t appeal to me. That, and the fact that everywhere I looked the proponents of NFP all had like 7 kids or something like that so I wasn’t (and honestly still am not) convinced of its effectiveness. I am not going to say I got confirmed being completely defiant and having absolutely no intention of following the teaching, but I was pretty close to that point. I’ve come around a little bit since then, but I still constantly struggle
all the time as I know I am not equipped with the personality to have kids running everywhere. But even though I still am very… unenthused, I guess you could say, with the birth control issue, I still love the Church and believe that it is an amazing gift to have in my life and just a wonderful way to live.
But point being, I would confirm this person if they show true devotion and willingness to obey in every other aspect of the faith. Believe me, if even I can come around a little bit on an issue like that, then this person can. I would talk to them more about the issue that they disagree with and work with them. You may be able to soften their heart, even if you do not see it. I don’t think one issue is enough to deny them the sacrament unless they don’t believe in Jesus or something.

I’m sure there are so many good Catholics that don’t agree/do not follow one teaching or so. I know many people on this site are
very strict Catholics, but we need to show a little mercy on people who are coming into the Church. This is SO hard to take in and a little defiance or anger at the controversial teachings is normal. Patience is a virtue. Find out why they are so opposed to the teaching and be sensitive to their thoughts and feelings. Hopefully they will come around.