"...it is said that someone at a party once asked the famous philosopher Ly Tin Wheedle 'Why are you here?' and the reply took three years." (The Light Fantastic, Terry Pratchett)
I am here because I got the invitation from Big Soft Moose.
Seriously, though: the question "why are we here?" is so open-ended, it's very difficult to answer. Where is 'here'? Our city, our country, our planet, 'our' solar system? :-\
I can offer three answers:
1. Being a humanist, I'd say we are here (i.e. on this planet) to help each other, to pick each other up when we're down, and to never do harm.
2. Being a scientifically-minded individual, I'd say we are here to inquire into the nature of the universe without having 'the divine' to fall back on. "Because a god said so" is not an acceptable answer.
3. Despite my scientific bent and rejection of the divine as an explanation for nature, being a spiritually-minded person, I marvel at the flight of birds, and the refracted light on rainbows, and the simple goodness that exists in everyone, if they open their hearts to it.
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As for the second question -- "should we be good?" -- again, this is very open-ended and imprecise. How do you define 'good'?
If we define 'good' as the opposite of 'evil' (in the classical sense), then being evil is no problem. It simply requires surrendering to all the baser instincts: sloth, lust, greed and so on. (The classical seven deadly sins).
Being good, on the other hand, requires self-control and perhaps that's why so many people have a problem with it.
For instance, they say: I'll go on a diet tomorrow. (Gluttony). Or: Ahhh, I'll do the work tomorrow. (Sloth). My neighbour sucks because he has a battery-powered spinning Santa on his roof and I don't. (Envy). The 'seven deadly sins' are why New Year's Resolutions exist.
Imagine if, instead, we all said: We don't need fancy gizmos to feel good. We are lucky to live in an prosperous age of plenty, in a place relatively free of disease, war, and want. We are blessed to have good friends and families who care about us. It is enough.