There are some good points, many I have thought about. For me, I'm more in the boat of it being much harder to get pg than I expected. My first took 18 mos. and we did TTA in between b/c I didn't think I could handle kids too close together, now that we're on month 3 of TTC, I'm kicking myself! What if it takes another year, or two, or more? What if I wouldn't have TTA, would I just now be getting pg after 14 months? Who knows! I know this is a silly comparison, but to me it seems like a girl and her hair. I had straight hair and always wished it was curly, my friends w/ curly hair wished it was straight! I have a friend who absolutely loves her 3 boys, but two out of 3 were conceived on BC, different types, while I'm worrying whether I will have another baby or if they will be 3 years apart or 10. When I was trying with my 1st, there were other girls I hung out with and they were all younger than me, married less time, and got pg w/o trying. One other girl and I were both trying w/o luck, so as selfish as it may seem, at the time I didn't have a whole lot of sympathy for the girls that were "oh no, what am I going to do w/ a baby", although I never told them I temporarily resented their ease at getting pg and we are still friends.
As far as family size-as long as you can handle your kids, financially, mentally, physically, whatever, and can give them the love and attention they need, then I'm all for it. We don't know, and don't need to know, ppl's motivation behind how many children they have. Maybe the ppl that only have 2 pass it off as the cultural norm, but in reality, that's all they can handle for whatever reason. If our parents had decided to stop one child sooner b/c it was easier, cheaper, more acceptable, whatever, we wouldn't be here. I know, state the obvious!
As for the financial aspect, I think it's greatly a matter of choice. To some ppl, $30K is enough for a family of four, while others can't stay out of debt w/ no kids and a $200K income. I know, there are circumstances beyond our control sometimes, such as getting laid off or having major medical bills, but like someone else said, we don't have to have the big screen TV and the brand new furniture. Babies don't necessarily need to wear baby gap and nike and have $600 of toys for their first Christmas. They need clothes and a cardboard box or tissue paper to play with.

Finally, I think some ppl are just "meant" to have many children. My aunt & uncle have 8. They were actively TTA after #6 due to multiple complications, including life threatening hemorrhaging, but apparently the Lord had other plans for their family and they are just as happy w/ children 7 and 8 as they were with their first. They are wonderful parents and their children are provided for.