Or do I just have to take it on faith that you would actually do good works because you care about people?
You may, if you like.
And why are your motives better then a Christian that has love of God in his heart?
I can only answer such a generalization with another generalization, and that is: Perhaps our motives are better because 'the love in our hearts' does not allow us to justify hatred or wage war against those who disagree with us, as often has been the case with "godly" people throughout history.
I do not say that all religious people are war-mongerers, any more than I would say all atheists are peacenicks.
That would be a generalization I could not prove, although, as Gopher, who tends to write in complete senteces, has suggested, much violence throughout history has been perpetrated by and through "godly" authorities, drunk with the so-called "love" of god.