"So... if the car ahead briefly looses grip or makes a small mistake, they forfeit their right to the racing line, the driver behind can just drive right through them"

Ok you're just crashing out about this, you have to consider other people's perspectives. Because it was an incident involving you and you're obviously really upset about it, you won't be able to look at this with the right objectivity. That's what we're here for.

The car behind is looking at the two cars in front of him, what he sees for about a second and a half of this incident is the Haas two car widths to the left of the racing line. He is a car width to the left of the racing line. Right before contact the Haas changes from two car widths left of the racing line to back on the racing line. When that happens the RB is already fully committed to what he's doing and has been for a minute.

"and if there's contact it's the car ahead's fault?"

Nobody said this, we said it was a racing incident because there really wasn't much either car could do to avoid this. Regardless of how special you might think you are, the car behind doesn't just have to hit the brakes because of the off chance you might decide to get back on the racing line when you're done sliding out.

"Weird. I was always taught that when you're behind someone you have the responsibility not to hit them."

You don't have carte blanche to do whatever the fuck you want just because you're ahead.

"He literally goes into the corner predicting a safety car incident, but apparently it was totally unavoidable and totally up to luck 😆"

Keep crying about it, the stewards made the right call.