Depends on what you call Public. I don't think one should kiss in public to attract attention. It is not about Indian Culture or anything... But Kissing or any act for that matter must be according to the situation. For e.g. Why do we say not to blow horns in hospitals or talk loudly in libraries. We are just respecting the situation and the people who are in it. However, If you kiss your beloved while bidding good bye at the airport, I think it is O.K.