In a very recent article of his,
Leonard David wisely and soberly reminds us once again
not to underestimate some specific side effects
of sending more and more objects and chemical substances into space,
because too much of what goes up
may come down and harm the atmosphere of our planet.
As he says " ... there’s a line of research that needs exploring:
The overall impact of human-made orbital debris, solid and liquid propellant discharges,
and other space age substances that reenter the Earth’s atmosphere."