God, I really hope this doesn't come to be. No offense to the people excited by it, and I totally get the appeal, but this would damage society so much. People taking performance enhancers, especially to extreme levels, put themselves insanely at risk medically. If this gets normalized, it'll only be a matter of time before it becomes mainstream to bet on blowouts, heart attacks, roid rage scandals, etc. At that point, it'll essentially be a tiny leap away from the game shows of Running Man, and then I'll lose all faith in humanity.
That's a somewhat fair question except that we learned about the medical side effects over time after the sport was established. Now, if people started trying to specifically bet on the over/under on CTE or if UFC got rid of tap-outs, I'd equate it a bit more.
The fact that there has been growing concerns and increased societal pressure to do better regarding the health of athletes, anything that poses them more as sports-creatures who should be willing to die for their profession could lead to significant backsliding.