I cycle around a local park where sometimes men fly or attempt to fly radio controlled plains and helicopters. I'm always wary of one of these objects dropping out the sky and hitting me! Isn't there enough crap flying through the air already,without you firing a stupid rocket up there for no reason? Stick to cycling it's cheaper,better for your health and more environmentally friendly!
You are more likely to be hit with a plane or a helicopter as they tend to fly in the horizontal plain sometimes at head hieght. Their uncontrolled collisions with the ground or people tend to be at high speeds. The Motorised projectiles also tend to be heavy meaning that there's a lot of kinetic energy waiting to do a lot of damage to anyone hapless enough to be the involuntary target. Having said that the number of serious injuries to bye standers is incredible small more through good management by the BMFA than through good luck.
Rockets, the small ones that get launched in parks are small, light and move in a vertical direction on launch and their descent is controlled by a parachute, or in the case of the smallest by tumbling or by deployed ribbons - imagine being hit by a tube a quarter of the diameter of a toilet roll core and 60-80% of the length. Larger rockets are launched from private sites away from densely populated areas and once again vertical trajectories and descents controlled by parachutes make injuries improbbable.
Your fears are unfounded. As for dismissing rockets as stupid that's both stupid and intolerant.