Its really disappointing to read the comments posted here. It seems we still need time to get grown up. Its not the 'kissing in public' which is bad, but the mindset with which we view the same is bad. This is a very natural and decent way of showing affection towards your partner.
Have you ever thought why it feels good when we see a mother kissing her baby? Or a newly married couple kissing each other in a church? It never raises ones eyebrow. It feels good. Because we know that it shows their commitment and love. Its not the kissing in public which is bad but the way it is done and the way we view it is wrong.
