I think it speaks well of you as a person that you are asking the question. It does feel a bit crapy to do it to someone, I agree. Before black Friday I used to play a lot of HU SNG's on Stars. I've waited for people to come back a couple times when they disconnected, but I stopped. The thing is almost no one else will to this for you thus you're giving your opponents an edge if you wait for them. You gotta just take advantage knowing that you'll be on the bad side too so it evens out in the long run.
Like I said it's a form of variance.
And also keep in mind, poker is a negative-sum game so to survive in it you cannot play clean. You are competing against both your opponents
and the casino (rake/fees), so you must take any and all edges you have and are are given, short of cheating.
In a sense poker sort of encourages scummy behaviour because it's necessary to survive. You don't play equally-skilled regs in a sporting manner, because that is a very significantly loss-making proposition -- you will break even so the only winner is the rake. You find bad players against which you have an "unfair" advantage, and you punish them mercilessly for their shitty play.