Who likes birthday parties? Especially once they get past the cute toddling stage. Twenty 4-8 year olds hyped up on sugar, screeching and farting. Hell on earth. We flip a coin. I'm hoping DS will be happy to be left at parties soon.
Ahem.
There's two (or three) issues in your post really.
Is it okay for dads (or mums) to dislike certain parts of parenthood? Are we supposed to love every minute? Are we bad parents if we don't? I don't think it's the case. Of course you're not going to love every part.
Secondly is it okay for dads (or mums) to have time off away from the family? Sure, I think so, but of course it has to be equal and balanced. And you can't both have so much time off that the children don't get any time with both of you, unless you're divorced. (I think it was Arial Gore who said "Bring me shared custody, hang the divorce!")
So really you're asking the third question (I think.) Is it okay for dads to partake in less or none of the stuff they don't like while the children's mother has to do more or all of the parts she doesn't like? No it's not, but it is definitely a sort of cultural norm. It shouldn't be, and I think mumsnet is brilliant for pointing out that this doesn't need to be the case and that a lot of men would be horrified at the thought of their wife drudging through loads of stuff she struggles with or doesn't enjoy just so he doesn't have to, but you can't ignore the social and cultural norm, that mums just have to suck up all parts of childcare (and are supposed to enjoy it all to boot, and are judged lacking if they don't), whereas men effectively get a free pass for not enjoying some parts of childcare, and a free pass from doing any part of childcare that they don't enjoy, on the grounds that women love every part, and men "aren't wired for it". So, similarly, socially it's acceptable for men to have more "time off" because they "need it" whereas women love children so much that being around the children IS relaxing to them - and also, being a SAHM isn't really a job or hard work, so what does she have to relax from anyway.
Cultural norm = reality for a lot of women, acceptable for a lot of men. It's not acceptable, in any way, but our culture says that it is, so a lot of people will assume that it's normal.