Why do people believe in and why do they do it?
(A preface is this kinda' offers hints toward 'Black' magic firstly then on 'white' if one believes in those. Perhaps that offers morality between good vs. evil.)
Perhaps the answer to those two questions is Reality? I know, I know not a real answer, yet at question is 'Reality'. One may make the leap to Freud's Reality Principal for understanding. That is the conflict(s), alignments, and questioning between one's "reality of the external world' (Other than self) and the pleasure principal". Thus, now, we must decide between 'Love' and 'Lust' with individualized meanings, coupled meanings, and, too, of those outside.
When pondering love potions what comes to mind are aphrodisiacs. Those are most usually a 'one - on - one' type of love potion. There are of course 'spell's' supposedly that could be cast too. Are those part of the discussion? Further is the purpose is to alter one's state of mind contrasting reality. Some make connections to the heart and soul too.
Of course as Lolita pointed out there is the connection to 'evil' no matter how you attribute it or name it. For instance is Rohypnol a love potion? A familiar one used within history dating to its inception is the 'powers' of wine to cause drunkenness with its consequences.
Love potions historically and within literature is well connected to seduction. To seduce means "attract (someone) to a belief or into a course of action that is inadvisable or foolhardy" while most usually means deceptively. A question is "What of consensual?"
That leads toward a 'next' possiblity. Can a 'love' potion be used in a congenial and accepted fashion? For instance a wife overtly hands her husband a familiar blue pill - viagra. She has been using 'Addyi'. That is a recently approved medication to enhance a woman's libido.
Maybe they have enjoyed a half bottle of burgundy wine at that point reclining before dancing flames in a fireplace - a setting for ??. Red wines are said to possess the power of being an aphrodisiac. Aren't those all 'love potions'?