Let’s put aside the shock factor for a second and really think about it. If Spider-Man shot cum instead of webs, it would open up a whole new dimension of character development and power dynamics.
First off, spiders don’t shoot mechanical silk from a gadget as they produce it biologically. So if Peter Parker’s mutation gave him realistic spider abilities, a sticky, viscous substance shooting from his body would be way more in line with nature. And what’s stickier and more biologically plausible than jizz? Exactly.
Secondly, it would make his powers more of a curse. Right now, Spider-Man’s powers are inconvenient at best: he breaks some furniture, misses class, and lies to Aunt May. But imagine if every time he saved the day, he was blasting ropes all over the city and then having to emotionally process that. That’s some true “with great power comes great responsibility” stuff. Psychological torment? Built-in.
Also, imagine the crime deterrent. Would you rob a bank if you knew a teenage superhero was going to swing in and bust on your face to stop you? That’s a new level of fear.
Finally, the memes and cultural impact would be unparalleled. You think “Thwip!” is iconic? Wait till it’s “Unnnghhh!”
I rest my case.