My father and mother had a love marriage, but now they are against me chasing a boy I like. How do I tell them that it is not fair?

I guess, there must be some concerns if they do not like you to be the boy you love. You should address their concerns and logically ask yourself that they hold true or not. Say, if they do not find that boy to be genuine, ask them why do they think so, or what led them to think this way. Being a parent, now I realise what parents are concerned about. They want the best to happen to their kids and that is why they want to doubly sure about whatever decision they take or their kids take.