Um. No it's not stupidity. Argh, and who cares if the person sucks in bed; you can teach them new stuff. It's not like I think with my vagina anyways and I'd just be happy to have someone to bang.
I'm waiting until marriage as I think it's smart instead of stupid. Look at how many girls are pregnant before marriage as they decided to "take a chance" on a guy they don't know well who later ditches them. Also, most new relationships don't last forever, so if the people have sex right away, it could stand that someone may get their heart broken (especially the female).
This may be the 21st century, but previous to the mid-20th, people were not supposed to have sex until they got married. I'd rather adhere to that tradition, as I want to be a virgin on my wedding night and know I'm with the right person, who wants to truly commit. It's like that saying: why buy the cow when you can get the milk for free?
Again, this isn't a personal attack against anyone. It's a person's own decision and I know someone people who aren't married are in stable relationships. I just thought I'd form a different opinion, defending... mine.