I will attempt to answer.
there are differing degrees of love spells, some are perfectly fine, others seem dangerously manipulative.
a spell to bring love to your life is an example of a good one. The spell is cast on you and it is only meant to help you realize love. It involves no one else (other people may be effected, all things we do create ripples in the pond).
a spell to make "wonderful" love you for ever and ever, never to leave you, is several degrees up the chain ( or down depending on how you view it) this is cast on a specific person, with or without their consent. this spell seldom seems to work as the caster intended. this is due to the fact that you are messing with another human, and well, humans change over time.
a spell to make "wonderful" leave their current "other" is just plain rude in my opinion. It causes more problems than it 'cures'.
a spell to make "wonderful" love you more than anything else in the world is counter productive, what happens if you tire of them? what about if they become mentally unstable? this is manipulation and I often see it as 'creating a stalker'.
In the above spells, "wonderful" is meant to apply to the person you have feelings for, it is also meant to apply to someone you have some form of relationship with.
Spells to make someone you saw one time 'love' you are ridiculous. The person in question has no connection to you, they may not even have any memory of you, so a spell to make them love you is not going to work.
Bring back my love spells are based in a need for control. Apparently the person you love doesn't love you if they left.
"I know he loves me, he's just confused" well, if your love is confused, Back off!
"She loves me but she is married to a horrid person who (fill in the blank about the sins of the other individual). I question the validity of this, or any statement were the person claims to know all the deepest thoughts of the other individual(s). You have to question the source of the information in these cases. Perhaps the one you love is actually the issue. Remember "love is blind", sometimes it is deaf and stupid too.
These are my own personal thoughts on love spells.