Not wanting kids is enough of a reason to abort. Not being ready, physically, psychologically, materially or whatever, or having enough kids already, are good enough too.
if i were female and pregnant, yes. if i were male (which i am) and pregnant (which i'm not) HELL YES!
anything short of genocide, that reduces human birthrate, preferably all human birthrate, across the board, without bias or exception, in an overpopulated world, is a simple and obvious yes. (and yes, earth has been overpopulated since about 1910, though its optimal population was probably much lower and previous even to then) (can you imagine what a paradise this earth would be, with today's technology, AND a population lower then at any time in the past three of four hundred years?)