I guess we were bad...
My family got a trampoline (my mom wanted one badly) when I was in (I think) 8th grade.
Big trampoline, no safety nets. On grass, but concrete nearby.
More than one person - elementary age kids, teenagers and adults - jumping at the same time (and "sending" one another - fun, fun, fun!) I think the most on it at one time was about a dozen.
Flips? Oh, yeah! Forwards and backwards.
And I recall my "daredevil" brother using the tramp at times with his BMX bike.
Best of all? Water, water and more water! Sprinkler underneath + sprinklers up above = a wonderfully cool and slippery wet good time!
Injuries/Accidents? None whatsoever.
Maybe we were just really lucky, but I wouldn't change a bit of it.
*I will admit, though, that my then boyfriend (now DH) sprained his ankle (and I
think a friend of his (ours) broke his foot) on someone else's trampoline as older teenagers.
All that to say this: I don't have a problem with trampolines. At the same time, I understand there are risks associated with them, so that's something each person/family needs to decide for themselves. JMHO.