Hiya!
I have no idea if/why people hate paladins. They are one of my 2 tied-for-first classes if I ever get to play. (Paladin and Magic-User...or "Wizard" in 5e parlance). I like the challenge...RP for Paladin, and "try-not-to-die" for the Wizard.
I've found that people who report to 'dislike' Paladins are the same type of people who dislike "level limits", "class/race limits" and who insist that Alignment is based on the PC/NPC's point of view. Not sure why that is, but I'd guess it's just a result of being brought up some particular way (actual Player).
I've DM'ed players way back in 1e who brought in their paladins from other games. Usually they end up making a new character after about 20 minutes of play due to them basically being Lawful Evil and me saying "POOF! You are now a Fighter". I'd get arguments, then I'd explain, then they'd "get it". Then they'd make a new PC...but not a paladin. They played a paladin for the power, and they used that power to lord it over everyone else...PC or NPC. Once they realized that they couldn't just kill random people on the street who detected as evil (or that even trying to detect evil on everyone they meet was Chaotic), they quit playing Paladins. Sure enough, their new PC would usually be a CN or TN Fighter, or maybe Cleric. Funny thing is...they'd play these new PC's just like they were trying to play their Paladin. Huh. Go figure?
I love paladins! I really enjoy playing the LG or NG characters. Hell, I recently played a Lawful Thief in BECMI (sort of a "DM-PC", because we are going to trade of DM'ing every couple months). He died,

, but he was fun to 'play'.
As it stands...I'm not nearly as keen on 5e paladins. They don't seem "paladin'ey" enough. They seem like "magical fighters". Probably because of the archtypes that are not 'LG'. I would have rather WotC called them "Holy Warriors" in 5e, and then made "Paladin" a separate class that had all the normal 1e 'trappings' (LG, Limited magic items, etc). But that's me, and I'm a die-hard 1e/HM'er.
^_^
Paul L. Ming