It's not about his opinion being more valid than hers. It's about their opinions being equally valid.
It's not simply a case of 'if they can live off one income then she automatically has the right to stop working.' There are huge pressures around carrying the total financial responsibility for a family. There may be worries (even if unspoken) about redundancy. There may be pressure to chase promotion and more money. There may be risk of burn out. Plus all the other curve balls life can throw.
Any major life decision should be discussed and agreed in a respectful relationship, not based on making demands or being manipulative.
The OP has every right to voice to her dh what she wants, and he has every right to voice what he wants, and that might be to not have to shoulder the financial burden single handedly. And if that's the case, then she has every right to expect more from him in terms of the domestic side of things... splitting days off if the child is sick, sharing domestic chores. That's how relationships between adults work, through honest communication and agreement, compromising when necessary.
MN is a bizarre place sometimes. You get the posters like @Anotherlongroad who try to hijack the thread by having a pop at WOHM and banging on about how they miss the precious moments (interspersed with posts telling us she's really not criticising!)
There's also massive double standards: a full time demanding career is either a easy ride compared with the stress of being at home with a baby, or it's something that's far too difficult and stressful to imagine trying to maintain - depending on who's doing the job!!
Ultimately it's up to couples as a unit to discuss parenting, working and running the home and to come to an arrangement which works for the family. There isn't a universally agreed or proven 'right' way. There are happy, successful and emotionally well adjusted adults who were raised in families where both, one or neither parents worked.
It really should be no surprise though that many couples choose an arrangement that isn't a clear cut earning/ SAH model. People often partner someone with similar levels of education, skills; with similar values and outlook. They often have similar capability of earning and of running a home. When I started living with dh, I didn't overnight become far superior at cooking or doing the laundry, and neither did he suddenly swoop ahead in his career. Likewise when a few years down the line we both decided it would be lovely to have kids, I didn't suddenly become an expert in changing nappies, entertaining toddlers or going to play group! We decided to both continue earning at a reasonable level but while the children were little, neither of us chased the kind of promotions which would have meant we had less time at home. As I said upthread, I'm sure if I'd stopped working, my dh would then have felt pressure to work longer hours or taken a promotion which would have involved travel... and they hey ho, a few years down the line I'd have perhaps been wanting a job but it would all have felt too difficult because we'd have prioritised dhs career.
So, in short OP- talk to your dh like an adult, and accept that if he doesn't want to be sole earner then it's really disrespectful and potentially very damaging to your relationship to try to pressure him into it. You're both parents; it's not something you have a monopoly on. Yes, as mothers we get the ML and may breastfeed but that doesn't confer special rights on you to give up your job at the end of your leave. And actually as an 'old timer' with 3 adult children, all very happy and successful and with a successful career of my own under my belt, I can honestly say that having children was the best thing I ever did, and maintaining my work life was a close second.