Compass
"[You're] playing at a table and the count is good. Player ask[s] if he should split his whatever against a 5 or 6. You should tell the guy to split but you know if you do the cut card will come out and you wont get another positive round in. You tell the guy to hit. Player listens. Is that evil[?"
No, it's not evil, it's just money flowing directly from his pocket to yours. Some people find this immoral, because it is happening directly and they prefer such flows to happen indirectly. Indirectly is whenever a clueless player sits down anywhere in the casino to play 21; his losses are financing your winnings.
Other people find nothing immoral in your scenario. They rationalize that the clueless player is punished for not knowing what to do "against a 5 or a 6" and also that, if it wasn't you, it would be some other, clueless player, who would give the wrong advice at least some of the time. Well, here it is, one of those times, provided by you -- plus, someone, i.e. you, gets to benefit from the wrong play.
It all depends on where your moral compass takes you.
(The generic advice is "Don't draw undue attention to yourself but try to blend in and act like every other casual player. If a casual player would give advice, and if he would usually give some specific advice, deviating from such advice draws undue attention." So, if you will give advice, you'll never advise, for example, to split 10s.)