how do you define 'harm'? this will determine if you view a spell as 'good' or 'bad'. I know people who feel curses are justified under the right circumstances.
yes, you love the person so much you decide to cast a spell on them to make them love you too because love is lovely. now take one step to the side and view the situation again. you want someone, and you don't care if they like someone else, or perhaps they are focused on other things than romance, would you walk up to them and say something like 'i know you aren't very interested in romance at this time, but i am, you're my boyfriend now until i realize this was a bad idea'. you wouldn't do this would you? however many people [specifically teen girls] do this regularly with spells. they have a crush they are too nervous to talk to, so they cast a spell to make fantasy reality. thing is, fantasy is rarely reality, so their wish/spell turns into a nightmare, so they undo the spell and they feel better. again, lets go from the guys standpoint, he went from at most a crush, to deep loving affection, to heartbreak, and it was the result of anothers desires.
are all love spells 'bad'? no [first i feel no spell is 100% good or bad] but you should think before you cast for one thing. spells designed to attract love, or when a couple cast a spell together [like a handfastening or an aphrodisiac] thats fine since either you're asking the universe to bring more love into your life [not specifically someone you know] or two people have decided to do something [therefore one is not manipulating the other] it's when someone [again, usually a teen girl with a crush] decides they want to date their crush, and instead of talking to the person, getting to know them, then asking them out, the person goes the 'easy route' and casts a spell to force the crush into doing all the legwork.