So! We can all agree that taking a nose dive into some mutagenic blood is a really really bad idea and I would absolutely agree with you, BUT-
The blood ocean itself isn't the issue even if it is irradiated.
The blood can mutate organic matter, yes, but WHY?
We know that the blood in the blood ocean is human but that doesn't explain why it's mutagenic and the possible radiation doesn't explain it either.
What I think is that when the Quiet Rapture happened, the god that caused it made only one of these blood oceans mutagenic and it's the one Simon is sent into. This ocean is able to mutate organic matter because a new group of cells has been introduced to it, we'll call them Morphocytes or "Morphs" for short.
Morphs are a group of cells that assimilate themselves into organic matter but the Morphs can't mutate or grow without DNA and RNAs so by itself it's just a mostly harmless (IF YOU DONT TOUCH IT) group of parasitic cells.
These Morphs NEED DNA to know what to make, so once they are introduced to, let's say human DNA then they're able to replicate the DNA.
Morphs behave very similarly to Cancer in how it behaves, but Morphs are radiation resistant because they aren't of Human origin or from the same origin of life that we know of.
Isolated Morphs will be in a constant state of change, unable to grow or build anything because they don't have DNA to build from.
Morphs are especially dangerous though because in humans they react to the stress hormones and can't regulate themselves so there's nothing to tell them to stop.
My friend and I theorised that the only reason Simon was so easily infected by the blood ocean was because he was blasting himself with radiation every time he used the camera in the SM-13, so his white blood cells weren't able to fight off the infection.
The only reason I did a deep dive into the science behind the blood ocean was because I was trying to apply logic to my BloodyMary fanfiction.