The fandoms angry reaction to Snowing doing a horribly bad thing is because they are our heroes and we feel betrayed (like Emma). Heroes aren't supposed to be weak or desperate. They are supposed to do the hard things not the easy things! That is what makes them heroes!
But even heroes aren't perfect, not all the time. In the same way that villains are not evil all the time. Captain Hook saved Aurora's heart, Rumple let Robin live and heal Marian, and Regina loved Henry.
Who you are is not defined by one bad act or one glorious good deed. That's why Rumples "redemption" by killing himself wasn't enough to change him into a hero. Being good requires you to constantly make the right choice every day, every time, no matter what. And when you DON'T make the right choice, cause lets face it everyone screws up, you don't blame others for your bad choice. You take responsibility and you make amends. That's Snowing's next step on the hard path and I have faith that they will prove to be heroes by taking it.