I really don't understand how anyone can decide that not understanding why or how something so emotionally and psychologically charged is important to some people is REASONABLE. 
There are good VB and good CS experiences. There are bad VB and bad CS experiences. Actually, I don't think the manner of birth matters, particularly, but I do think that how a woman feels about the birth they have is fundamentally important to their future wellbeing.
So, OP in answer to your question:
AIBU to not 'get' why this is so important to them?
Then you're being VVVU indeed, in my opinion.
Because it really can be, and you should at least try and get it, if someone is talking to you about how they feel. It is the very opposite of reasonable not to.
But, to lay my cards on the table, I think a good VB, if it's what the woman wants, is generally a more positive experience than a good CS - even just in terms of recovery times and risk.
My experience is also that, even though it's definitely a painful experience (and my second was, but not agonisingly so, unlike my first) it can also be empowering and rewarding.
It isn't like that for many women, I know from personal experience, but I think it could be like that for more women if the support they received was better.
But I also understand that it's also not something all women want to do, because I have made the effort the get why that may be the case.
No-one should make someone feel bad about the birth experience they have, but equally no-one should make someone feel guilty or ungrateful because of how they feel about the birth they had.
Surely as mothers, we owe it to each other to try an be understanding of the complex emotions and feelings surrounding birth, of whatever kind?
That's the reasonable thing to do, surely?
db
xx