Are you guys really in shock about that?
There is such a thing as pre-cum.
Sucking raw dick exposes you to that. Because there's no set time for when those things can secrete into your mouth. It varies from person to person, aside from the obvious big final ejaculation.
If you have any open cuts or sores in your mouth (that you may not even be aware of), it can seep through those openings and infect you. There are so many sexually transmitted diseases you can get from unprotected oral sex.
Don't be so quick to just pop anyone's penis into your mouth. There's a reason flavored condoms were invented.