Underwear offers a barrier that keeps residual urine and feces particals from absorbing directly into your pants.
People that dont wear underwear let their bodily fluids make direct contact with their pants, and then expose them directly to any surfaces their bits might touch.
Not wearing underwear is unhygienic.
Oh homie, everyone is covered in pee and poo particles every time they flush a toilet. Also, urine doesn’t just magically stop at the undies, it absorbs into pants too.
Humans are animals, and we are constantly exposed to pathogens and waste just like all the other animals. Wash your hands before you eat, and keep your food contact surfaces clean. Beyond that, don’t worry too much about all the incidental contamination you run into, it’s largely out of your control and knowledge anyway.
I see posts like OPs, and hear people saying such things IRL, and I always think, “This person would straight die in a week if they faced the most minimal survival situation.”