Only one STD is both incurable AND fatal, and that is HIV, which can be prevented with proper condom use or requiring partners to be tested before having sex. There are a little under 50,000 new cases of HIV every year, a scant .2% of the 19 million infections contracted yearly, and representing .1% of the American population of apprx. 317 million people. (That's one tenth of one percent, not one whole percent, in case you're a little math rusty.)
All other STDs either cause discomfort that can be alleviated with medicine, or can be cured outright.
According to the CDC, in 2008 the deaths caused by HIV were 4 per 100,000 people, or about 12,000 in the whole country. According to the National Highway Traffic Safety Administration, in 2008 there were 37,261 deaths by car crashes.
So, if we're going to base our morality on unintended consequences, why isn't anyone else declaring driving automobiles to be immoral? Clearly the death and pain caused to tens of thousands of families yearly is a sign from god that we were never mean to move faster than we can run!
Our attitude towards it in modern times ranks among some of the most disgusting and self destructive attitudes towards transportation ever.