We were both sportsbikes riders before I had my baby. In fact I rode my Kawasaki ZX6R in SE Asia to work and back until I was 4 months pregnant, and that was only because the bump got in the way of the tank.
But having had my daughter, I'd be reluctant to ride again. Even a push bike.
My risk profile has dramatically changed. Plus I don't really have the time to do separate things. It would be nice to get into work easily but riding in London (I have years of town riding experience and advanced riding on a range of bikes) is risky. I reckon actually riskier on a pushbike because you're travelling at a different speed from other road users and aren't so visible, but that's another issue.
I understand the appeal and really I suppose he can consider your feelings but that ultimately he has to make the decision. If he feels he hasn't made an informed decision, he may feel resentful. He should also be aware that it takes away weekend time from the family (he may argue that he needs his space, but don't we bloody all - can't have everything, lovely kids AND loads of free time...)
For what it's worth, I rode every day on a mentally fast bike in town and in places like Malaysia for about 12 years and apart from the odd minor slip never had anything happen. My husband was a bit unluckier (funnily enough on trail bikes) and broke two limbs.
He's still got a 1970s classic Bonneville that he will ride this summer, but it's not reliable enough to ride to work.
Could he get a sportscar instead? That's what we did, got a creditcrunchtastic Porsche 911 -- we can all use it then, plus it's safe (if you don't drive like a loon) fairly fuel efficient, you can get a britax in it. But it helps that the front passenger has no legs....
But could be a way to tick the mid-life-crisis box in a way that isn't totally unsafe and that you can use too.