Scary part is most don't show symptoms. I am even talking about the worst one of all- HIV which later manifests into AIDS. That's a serious one.
Sucks because I would love to have sex with tons of people but the risks aren't exactly light.
During the mid 80's is when people had to start getting serious as that is when HIV first became a large issue in the US. Before than we were actually having good sex- humping like bunnies- and rightfully so. Sex is awesome!
I think we are making headway into the AIDs epidemic now though. Before HIV was a death sentence. Usually you could live about 6 months to a couple years at the most. Now we have suppressant drugs that keep the virus in check and if patients remain healthy/fit than they can live long productive lives.
The rest of the STDs are no biggie. Rashes, worts- pretty minor because hey, at least you won't die from it and often times the problems begin to fade by themselves. Herpes outbreaks reduce over the course of time because the body begins to find a way to fight it. If you get syphilis then you just need some penicillin... as long as you havn't progressed past the 2nd stage or the latency stage then you might be due for some mental retardation or deformity.
Stay safe.