First, that sounds awful. Glad your're okay.
Second, I don't think we're talking the same scale here. A sport game has several thousands of fans, lots of them wanting to storm the field. It's pretty much a completely different job guarding that and a presentation with (presumably) way less people and way less room for people to storm and overwhelm the security.
I'm not a security expert, so I might be wrong, but that just seems to me a whole different scale which is harder to implement.
A monopoly isn't inherently bad, but a monopoly by a state is pretty bad. It means they can exert political pressure over you using that sector's influence.
Heck, look at Russia and gas. It impacted tons of people all over the world, and if the world hadn't collectively said "fuck you Russia we'll handle ourselves without you" - then countries like Germany wouldn't have a choice but keep buying Russian Gas.
That's a political power you really don't wanna give to anyone, especially not China.
Yes, competition could restart, but that'd take time. And you don't always have that time. Again, see Russia and gas as a nice example for that.