well it appears i misinterpreted what you were saying then, in the original post i responded to it came off as if you felt - in a way - nice guys were kinda entitled to sex, because we all feel entitled. but you've clarified this, so my apologies xD
as for whether it is bad judgement or dickheadedness, i suppose it would depend on their attitude towards it, for example
person A: "i was really nice to her, but she only saw us as friends so nothings gonna go on there. kinda sucks, but it happens"
person B: "i can't believe i spent so much time listening to her whine about her stupid problems, and she wouldn't even fuck me?! it's bullshit"
they could have put in the same amount of investment, but because of their attitudes about it person A i would say is the misguided one, whereas person B is a dick. a misguided dick, but the dick quality is still the quality most easily recognised.
as for safe ROI for sex being a prostitute, definitely agreeing there. it's only the form of investment that changes, from time/effort to money (which arguably is made from your own time and effort anyway, but that's getting a bit too off-topic). regardless, the return is at least guaranteed