I have been a SAHD for 11 years, since DD was born. DS is now 9. Nothing wrong with looking after your kids yourself, particularly when they are pre-school, and there's no reason a dad can't do it as well as a mum.
In our situation we are able to do it as my DW has a good job - we don't claim any benefits except for CB, we don't rely on the state or wider family for support. It's not megabucks (we are not higher threshold tax payers), but it's enough for us. For us it was a conscious decision for me to take on the role, and we found when the children started primary school that we wanted to have one of us there to drop them off, collect them, take them to after school activities, etc. And DWs job is quite stressful, so I enjoy being able to run the home to make it a good place to come back to after a mad day at work.
Career wise it has pretty much wiped out what I was doing before, but I have compensated by running a small business from home which can be done while working around the family. I also have a very part-time job, which lets me do admin work, again at home and fitted around family commitments. You might say this is a waste of my education (3 degrees), but my education was more about forming me as a person, not just training me to earn cash. And I don't have any student debts - in fact DW and I don't have any debts, we have been very careful and sensible over the years.
So to answer the OP, no reason why someone can't be a SAHD, just as there is no reason why someone can't be a SAHM - there is very little difference between the two. Your OH needs to be clear about what effect it will have on his career, and how that can be managed in the long run. He also needs to be honest about how he would cope with the role - being a SAHP can be isolating, being a bloke in the role can be a bit more so (like, being the only chap at a toddler group). But it's not impossible, and I have found it very rewarding. Because society assumes that if anyone is going to look after kids it will be the mum, I view my parenting role as a real privilege, not something I am stuck with as a default position. But that is because we have been able to make a conscious decision about it, and DW and I are very close and supportive of each other in the different roles we play.