Trivial answer is "I'm not being kind because I necessarily expect reciprocation, I'm being kind because I genuinely value other people's well-being".
But that actually depends on your meta-ethics. Some people would say that they are only good for selfish reasons. I think it's a rationalization, but hey, who cares as long as they rationalize themselves into doing good things.
In the Christian worldview, yes, we should treat others as we want to be treated since they are created in the image of God.
That isn't a reason, that's just words. Why would 'being created in the image of God' imply good treatment? It's the is-ought problem all over again: that is a fact that doesn't imply a moral obligation without some further moral framework that says 'that which is created in the image of God should be treated with kindness' or words to that effect.
Should you be good to get to heaven? Then, as Star Cluster pointed out, that's still a selfish motivation.
Do you get to Heaven because of grace regardless of being good or not? Then what the hell does Christianity have to do with morality?
Does grace make you do good things because you are one of the elect (as some Calvinists hold)? Then Christianity doesn't really account philosophically for morality, it just says 'magic ghost came and made me a good person'. Which makes it irrelevant, because non-Christians also do good things.