not fundamentally different as in "live or die" you mean? the whole point of sports is that you compete whilst appreciating each others' humanity.
"The whole point of sports (in my opinion) is X good thing therefore betting on sports is more acceptable"
Making bets on good things doesn't make the betting better. Just because Polymarket would allow you to bet money that the infant homicide rate goes down next year, doesn't mean it's a good thing to allow betting on.
The same can't be said for war (bombings), which Polymarket allows betting on.
Seems like a fundamental difference to me.
one is more culturally taboo than the other, but they are fundamentally the same activity
If you have a point to make about how the age of the person being murdered means it's a categorical difference rather than a difference of degree I'll read it.
Eg, to be rid of a turbulent priest, you'd place a bet that Thomas Becket will live to see the year 1171, which is a "good" outcome to bet on happening.