It's all good and well saying a man has the freedom to do as he wishes, but how do you know what it is he wishes for?
Yeah... this. I know there's certainly many men who are happy to swan off. But do a Google search and you'll see there's a flood of news articles, agony aunt letters, message board posts etc, etc from men who feel unable to get the access to their kids they feel they should have. It's a widely given reason why men often don't leave the family for the OW. Why? Because there has, up until now, been the widely held belief as stated in this thread and others: that kids "belong" with the mother and that she is the most important parent. Dads are just an optional extra.
I can only put forward my case as a (possibly exception to the rule) example:
Ex-wife decided to quit her job to be a stay-at-home mum. I wasn't keen - I actually offered to cut my hours to allow her to work - but she insisted because she felt it important she "be a proper mum".
She didn't enjoy it entirely, as I suspected. I offered support but she felt I was treading on her toes. She actually said "are you saying I can't do it myself?"
Upshot was she then felt entitled (this came out in counselling) to have an affair. Because she'd been putting so much in for others (the kids) she felt she was entitled to be a little selfish for once.
we didn't recover. She felt I was surplus to requirements. But she didn't ask me to leave - just continued on with her affair and not even really bothering to hide it, until I caught them again and felt I had to file for divorce. She didn't show any remorse. She just got angry - the audacity I had discovered them together rather than turn a blind eye - and replied "whatever" when I said I would see a solicitor.
The divorce itself was surprisingly amicable. I bit my tongue for the good of the kids. I still do - she won't tell anyone bar her best friend she's sees the OM still in secret, even though he left his wife too. But she told me I should only see them every other weekend because that was the usual arrangement. So even being the cheated upon partner, I was told to accept an arrangement where she did most of the work. Because she saw that as the woman's job and the mother's role. Not mine.
I didn't accept it and fought for a greater share of parenting. Its still not 50:50 as I work full time and she doesn't. Its her choice though. We could arrange it if she wanted to. But she doesn't.