In a real scenario, the unknown individual asking you for sex has a high probability of having an STD or some psychological disorder that causes her to push men away, i.e. BPD et al. If you were handsome, she wouldn't be on your radar, considering the selection you would readily have and already enjoying; if you were not, then the odds of her having an issue where she cannot attract a more handsome man rise exponentially. You can avoid an STD through condoms, but you cannot avoid a bipolar nut who wants you harmed as she did not assume you were interested only in a one-night-stand, or otherwise ignored your sentiment and demanded the conditions change after the deed. Anyway, chances are high that she will deny a test of any sort and instead go to the next guy who is willing to put out, either because she would not want to be found out or is too impatient to wait for someone who really wants her--and probably both. The trap is inescapable, outside of the straight answer that is "no".
In other words, those who are saying yes should consider how much value they're attributing to their lives.
Exactly.
You say yes...
Next thing you know - you are lying in a bathtub without a kidney.