Why Are Big Families a Bad Thing?

My husband & I both come from large families. My husband is #10 of 13 kids while I am #5 of 6 kids. Together, we have 7 of our own children - 5 boys and 2 girls. I am currently 13 weeks pregnant with #8 and we plan on this being our last baby. Anyway, since announcing my pregnancy I've gotten MANY negative comments. Both of our families are thrilled but others - not so much. I'm already starting to show and yesterday at the grocery store - with only 3 children with me - the clerk looked at me and said "Why do you have so many kids? Aren't you worried about the economy and our environment?" I don't know if I'm overreacting, but I found that to be quite rude. A few weeks ago we attended a New Years firework show and had all 7 kids with us. You couldn't see a baby bump under my coat, but yet we had many comments like "I bet they're on welfare", or "That man must work really hard and get rewarded very well". What is wrong with people?! For the record, I am a stay at home mom. My husband is an orthodontist. He makes great money. We have one credit card for emergencies only. We are not on any form of welfare. We actually have a decent savings account and we own a 6 bedroom home. We take our kids on vacation every year. I'm blessed to get one day a month by myself to go shopping and spoil myself. So if you haven't already gathered, OUR KIDS ARE WELL PROVIDED FOR! I just want to know why it's viewed as a bad thing to have 4+ children in today's society.