Sorry - this is a long one....hope you are still awake by the end !
I really sympathise with you MBB.
You may never be able to make your husband understand, but agree that you need to try to get to the bottom of this. Especially, since he has changed his mind - whatever you decide is the right thing for you, you will need his full emotional support.
IMO, in general, it is different for men. Much as they love parenthood and may take a very full role in fatherhood, they don't have the hormones coursing through their body and they didn't carry the bambino for 9 months. Also, in general they haven't just had an extended period at home with their child - doing everything for their baby day in day out, forming new friendships with other mothers and babies and getting into a routine. And they don't have the underlying cultural pressure that "good mothers stay at home with their babies."
Also, I think that some fathers find it a little hard how much their partners change especially in those early days. Naturally, the baby becomes the centre of the universe. If the mother used to work and have other interests, the father could find that adjustment hard to start with. They may look forward to the day when their partner regains the balance in her life. (It may sound selfish but it is understandable.)
Also, maybe he is worried about having to be the only breadwinner. So few jobs have real security these days and different people have different tolerance for risk. If you were able to show him how you will both budget and manage on his salary, still pay off the mortgage etc, maybe he will feel more comfortable.
I wouldn't worry about what other people say other than your husband - unless they are very close friends/family who have gone through this themselves. Then it might be worth listening to what they say and just considering it. For some people it is " just a phase" and some people don't have a feeling of self worth unless they are in paid employment. Only you know yourself well enough to answer that for you, but I found it very difficult to answer that question in those first few months. Work was so unimportant when compared to the miracle I was part of.
I went back to work when dd was 14 weeks old, after the full maternity allowance I was entitled to (we live overseas.) I dreaded it and only went back because they were about to eliminate my job. As the pay out would have been quite a lot of money we decided I would stick with it until they made me redundant. In the end, they also offered me a part time option - 4 days a week. I decided to go for this for a while and see how things went. I found it much easier than expected and now my dd is 18 months old, I'm considering going back full time (to do a new job) although we will probably move closer to my office to completely eliminate travelling time.
I won't say I find it easy all the time (I don't feel the same about work as I used to), and I sometimes feel jealous of the time some of my friends spend with their kids. But I know that some of my friends feel jealous of the time I spend at work, so I reckon you can't win either way.
After a few months back at work, I realised that I'm not the kind of person to be able to stay at home to look after her all the time and that I benefit from the time I spend at work. And the critical thing is my dd is a very happy, secure and loving little girl, who has a great bond with me and my husband. For now this works for us. We aren't commited to this for ever - we will change as our needs and her needs require
Is there any way you can keep your options open a bit longer? Some companies would allow a career break or some additional unpaid leave. You don't mention what kind of work you do but if there is a possiblity of some kind of part time arrangement, (not the 9 - 5pm, 5 days a week that you mention) but perhaps 2 - 3 days a week and maybe working from home a bit, it might be worth exploring. It would give you a chance to see whether you really want to change course or whether a mixture may work for you.
HTH, and good luck with getting to the bottom of your husband's feelings and with you reaching a conclusion that works for you.