I was told that getting a smiley piercing is not worth the pain plus it would likely be torn off by kissing etc which I think is stupidI dont understand how if its on the inside of your lip?

It can be torn off while kissing. It is very easy to do if the others person teeth pulls on the piercing. Kissing is also advised against for people with a smiley piercing because of harmful bacteria that could infect the piercing.