As a rule, there is no such thing as charity and compassion. Most people are in the business of "helping others" only to receive something in return. I mean, think about it. Some have even made the betterment of others their career! Therapists, counselors, doctors-- all make a living off of the rest of the world's problems. That's not to say that what these people do isn't valid or right or worthwhile. It is! But they're not really doing it out of true concern.
However, this doesn't just apply to people who get paid to help. Ever volunteered somewhere? You did something for your community. Good for you! But you probably felt pretty good about yourself afterwards, didn't you? That doesn't negate your impact.
Even Christians, who, according to our own rule, should be the most charitable and compassionate of pretty much anybody (but sadly, often aren't), don't give from the pure place of wanting to see the other person happy, and nothing more. We are instructed to give in Jesus' name, that we might bring honor to Him. This isn't a selfless cause, no matter what your worldview might happen to be.
Is it even possible to do a single selfless act? is it part of our human nature to have an ulterior motive for everything? or are we only supposed to enjoy the feeling of fulfillment (and possibly, self-righteousness)?
I won't refute anything you've said because you're almost completely correct. I must disagree though because it's possible to transcend human nature in some ways. A person can commit a selfless, helpful action. It really is possible, but highly uncommon in this day and age.