personally i don't cast love spells, don't feel you should force something like that.
ethically speaking, it depends if the spell is asking the universe to bring love into your life and asking the universe to make John Smith love you. one, you're asking to meet someone, the other you're forcing them to feel the same way. both these spells do work, one's harder than the other, some people feel that it goes against the Reede since you're imposing your will on another and therefore doing harm.
if you cast over a person, this one is harder because everyone has their own free will, some people are strong than others. the spell you cast must be stronger than the persons free will, but keep in mind their will shall always be fight back against the spell subconsciously, so one day, they might wake up and no longer love you. some people will constantly recast over the person to keep them. and this isn't really love. it just comes down to what you feel comfortable with.