why smile?

I received this comment on facebook:
‘You are aware, that you can do that only for a limited period of time...sooner or later you will get fed up with all the unsubstantiated smiling, and when that time comes and you have nothing to fall back on, nothing you built over time well...you'll simply be miserable!’

This was a post regarding my description:
I am the girl who smiles even though her heart is broken and the one who can always brighten up your day even if she couldn't brighten her own.

My answer was:
I have been smiling for more than 3 years now and I certainly do not fell miserable. It's not a false smile cause it comes from inside. That is because I consider that life is not all about money and everyday problems. We need to value what we have, we need to dream, we need to achieve our goals, and we need to be happy that we know people that care about us. I've experienced broken dreams, people being mean to me and I've been disappointed by friends I care/cared about. I am still smiling because life and time won't stop to help me recover or just because I'm sad. So I have to choose between being miserable and feeling pity for myself and trying to get over and smile again. I consider that at the end of your life you should be able to say that you did your best to live it, not that you were brought down by all the problems. I will continue to smile, but not unsubstantiated.
As I said before, I have reasons to smile for: I enjoy my senses (although for normal people seems something right to have - I can see, I can hear, I can walk and so on), I have a family that loves me, I have friends that care for me, I can enjoy university life. Why to be sad? Why not smile? Why? Do you think it is better to be sad or just ok? I don't sustain that I’m smiling all the time, because I have my moments of sadness and concerns, but I also have friends that help me get over. That is why most of the time I am the girl who smiles... Maybe I haven’t had too many problems in my life... But 4 now I have enough reasons to keep smiling so I won’t be miserable. As for the ‘you have nothing to fall back on, nothing you built over time well’ I do have something: I have my friends that know me as I am and will always be there for me. If you approach it in pessimistic way (which is not my point of view at all), if all my friends let me down, I still have my family. If my family won’t be there for me, I still have my mind, my skills and my way of being to start it over or to recover. SO is this enough 4 you to change your mind? :)
So will you smile more now?