We taste a lot of different chemicals as bitter, including cucurbitacin, persin, quinine, solanine, strychnine, momordicin, cyanide, and benzaldehyde, and consequently amygdalin. Apparently we have 25 or more different bitter taste receptors sensitive to more than 500 different bitter chemicals. The lethal doses of these chemicals in proportion to their bitterness vary enormously, and of course they also vary according to the situation: the momordicins in bitter melons are fine most of the time, but bitter melons are an abortifacient (possibly due to an effect of the momordicins) so you shouldn't eat them if you're pregnant. (There are other inexpensive means of abortion, such as misoprostol, which have been carefully studied and shown to be safe in the first trimester.) And different chemicals extracted from bitter melons have been shown to be cytotoxic in vitro and might be useful against cancer; some hepatotoxicity has also been shown. https://www.mskcc.org/cancer-care/integrative-medicine/herbs...
So I would say, no, they're not bad. But don't go overboard.
