Love at first sight is not a very realistic notion. Sure, you can be physically attracted to someone the first time looking at them, but you can't really love them until you get to know them. And that takes time. To truly love someone you have to be able to accept them, flaws and all.
Love is not easy. Ask anyone who is in a successful long-term relationship. You have to work at it. You have to make sacrifices and think of the other person before yourself. It means sometimes your relationship won't be 50/50. It will be 90/10 some days, and that is okay. The reason it's so hard is because it's been fed to us our entire lives that all we have to do is be like Cinderella by befriending some mice, waiting for our Prince Charming to find us, and live happily ever after. You never see Belle getting frustrated with the Beast for all of the fur being shed on the furniture or Eric complaining about how Ariel won't call a fork by its real name instead of some made up word.
You have to work for the good things in life, including love. It's toxic to think otherwise. Relationships fail because of these kind of unrealistic expectations.
So how can curses be broken by a complete stranger? They shouldn't be able to. Movies like Frozen, Enchanted, and Maleficent got it right. The people who loved them *because they knew them* were able to break the curse, and that's how it should be.