yes you should take STD's seriously but to use STD's as your reasoning for not having Casual Sex is the opposite of how you should be handling this.
What we need is proper education about protection, risks, and just sex in general not making people afraid of sex!
You could just as easily get an STD from the first time you have sex after a date as you could with Casual Sex.
Maybe, but people willing to have casual sex with you are probably also more willing than the median person to have casual sex with other people, which probably means they're likely to have above median number of lifetime sexual partners. Unless you're arguing that lifetime risk of getting an STD is uncorrelated with the number of lifetime sexual partners, I wouldn't so quickly declare the two risks to be equal.
Edit: I left the U.S. about a decade ago, and as I remember, they were considering allowing MSM to donate blood if they'd only had one partner in the past year. I was under the impression that was based on statistical risk modeling, but maybe it was plain old prudishness being dressed up in statistics. I still donate blood here, but I've lost track of US blood donation rules.
On the one hand there is the person that may have a lot of casual sex but they are also properly educated about sex, they get tested every couple months, they take precautions, etc. Maybe they are more used to having conversations with potential partners about STD's.
On the flip side you may have the person that rarely has sex, never really has those conversations with their peers or doctor and maybe only gets tested during their yearly physical.
And yes I know I am very strongly generalizing here. I know people in both camps that do the opposite of what I am saying here.
So that is why I say that yes obviously more partners increases your chance of getting an STD, but you also can't just say that because someone does not have a lot of partners that you can't also risk getting something from them.
Edit: By properly educated I meant about sex... not anything else. Making that more clear
Second Edit: Regarding the men who have sex with men blood ban, I think that has been proven many times that there is no evidence for it and is purely from a puritanical stance.
I think that's a straw man argument. My reading of the GGP doesn't include any claim that non-casual sex is risk-free, just an implicit suggestion that casual sex is riskier.
Though, the GGP isn't explicit about their claims, so I could very well be misreading them.
I have seen "sex ed" (in quotes because some places I would barely call it that), especially in the South, use STD's as a way to scare kids into not having sex which is so wrong.