The Bet in "JAM Session"
The bet in "Jam Session" is obviously a really bad idea.
It is one thing to predict that Piper will succeed or fail in her attempts to control her bad temper. It is another thing to bet on the outcome and thus become emotionally invested in having the outcome that one predicted happen.
A superhero shouldn't bet that something bad will happen. Piper is sort of like future supervillain material. So Ray should hope that she learns to control her temper and that nothing bad happens to her for a long time until she becomes less bad tempered. If Ray bets that she will lose her temper he will be tempted to do bad things to her to make her lose her temper.
Ray and Henry have shown signs in various episodes that they have villain tendencies and could do face-heel turns and become supervillians.
http://tvtropes.org/pmwiki/pmwiki.php/Main/FaceHeelTurn
So none of the other characters should want Ray to bet that something bad will happen and then be tempted to make that bad thing happen. That seems to be playing with fire.
Henry and Charlotte shouldn't have bet that Piper could control her temper. Knowing Piper, they knew she wasn't very good a keeping her temper, and they were running the risk of losing and having to do something unpleasant. Furthermore, they knew Ray enough to suspect that he would try to make bad things happen to Piper so she'd lose her temper.
By making the bet with Ray Henry and Charlotte thus ran the risk of:
1) Piper losing her temper, becoming frustrated, and giving up her attempt to control her temper, and thus sometimes making life miserable for Henry and Charlotte for years to come.
2) Piper losing her temper, becoming frustrated, and giving up her attempt to control her temper, thus increasing the probability that Piper will become a super villain in the future.
3) Ray following his evil tendencies one more time by causing bad things to happen to Piper to win the bet, thus increasing the probability that Ray will become a super villain in the future.
4) Ray following his evil tendencies one more time by causing bad things to happen to Piper to win the bet, and thus inflicting misery on a little girl trying to reform, a child who is a member of Henry's family and someone Charlotte has known for years.
Because of all these obvious possible bad results of the bet, it is almost as stupid and unethical for Henry and Charlotte to bet with Ray that Piper can control her temper as it is for Ray and Jasper to bet that Piper can not.