Some pairs of opposites, each with an identical number of letters:

love-hate

black-white

old-new

violent-passive

play-work

mind-body

brain-heart

head-tail

stupid-bright

yellow-purple

right-wrong

jungle-desert

rich-poor

loud-soft

hard-soft

cool-warm

good-evil

plastic-natural

real-fake

glue-lube

strip-dress

help-hurt

cut-sew

build-wreck

bind-free

good-poor

sick-well