Are you new to following sports or something? This fan reaction has been completely typical and expected, and, actually, is much milder than what you would find at an SEC or Big 10 school. I believe Tennessee and Penn State recently had student marches. Meanwhile, you're complaining about a few internet posters saying mean things.
Losing to FIU is a new low for a program that had already been rotting on the garbage heap. You can't equate that loss to a potential one to Louisville, and you can't dismiss or downplay it with hypotheticals. It was an abject failure - and an utter embarrassment to the university community, the alumni, and anyone who has ever worked or played for the university.
Diaz deserves the scrutiny. He signed up for it, and he's made his own bed. And it's entirely within his power to make it go away with a great 2020 season.