Because I know the sex education in this country is abysmal. This advice probably works for trans women and male people, but biological sex definitely plays a part here.
Just because a man or boy says they are “clean” (clear of STD’s) does not mean they are “clean.” Unless they really test for STD’s on a regular basis, when they say they’re clean, most likely they mean that they are not experiencing outward symptoms. I’m not saying they’re lying (although that’s also a possibility), I’m saying that there are a number of STD’s that are asymptomatic for male people but more likely to be symptomatic for female people. So even if a boy or man seems nice, even if you think he wouldn’t deceive you, I need you to remember that sex ed in the US is not universally comprehensive. If he has ever had sex with anyone before, he may have an STD and have no idea.
All this being said, it is not irrational for you to request an STD test before intercourse. They are free at many clinics like planned parent hood and you can discretely order them online or from the local pharmacy.
If a potential suiter is ever apprehensive about testing first, you should consider this a red flag. This is not about trust, this is about health safety.
This is advice for anyone of any gender identity or biological sex: no one’s feelings are worth your health. Many of these STD’s are forever. If someone threatens to break up with you over this, they are being emotionally manipulative and you deserve better.
Stand your ground. Protect yourself.