As Tova pointed out, it’s terrible, as it teaches children to disobey school rules.
Besides that, the entire series culminates with the heroizing and whitewashing of a truly bad man, due to his incapability of getting over his ex-girlfriend. A sleaze bag and jerk, who punishes Gryffindorers but give Slytheriners a free pass, Snape was a DEATH EATER who never changed his hashkafos. Indeed, he continued calling Voldemort the Dark Lord. But he begrudgingly agreed to save Harry, and betray his beliefs, not because he caused the death of two people, but because one of those people (a married woman) was his love.