The only thing I would say to this is when you're in the thick of it having young kids it's easy to get into the mentality of "what's one more"? You're barely sleeping anyway, or always making food, or doing laundry etc so crack on, but the thing is they grow up, and your life gets easier and suddenly having 2 kids is actually quite a breeze (and dare I say it, fun) but for those with 3, their lives are harder (not saying hard, that's subjective, but it's harder than 2). Financially it costs a lot more, in terms of time you're splitting yourself further and that reduces time with your other children, your partner or doing something for you.
I seriously considered a 3rd, I was really, really on the fence. But now I look back (mine are teens) and I think god I'm so glad we stopped. I really under estimated the value of time with the children as individuals, and look at those with 3+ more kids and their lives just look so much more difficult, I swear I'd just be a taxi!
To add to that I say that as someone who has a good amount of support, not on a daily basis as family still work full time, but they take the kids on holiday and have them for sleepovers and weekends occasionally which I credit the strength of our marriage on. Having even 2 without support sounds really isolating,never mind 3.
Life with babies is hard, it's not the most rational time to make that decision (though unavoidable!) but worth trying to really understand parenthood at the different stages, not just babies and toddlers.