But it doesn’t change the fact the people always act in their own self interest. Always.
That would be very compelling if it were an actual fact. Fortunately for mankind, and unfortunately for your point, it is not even close to an actual fact.
Here's the thing - as a generality, you're right. It's actually why progressive policies will never, ever work. Capitalism works because, as a generality, people are far more interested in their own self interest than anything else.
But, in the day-to-day of life, people do good things for absolutely zero other reason than it helps other people.
Dictionary.com said:
altruism
[al-troo-iz-uh m]
noun
the principle or practice of unselfish concern for or devotion to the welfare of others
People practice concern for the welfare of others on an daily basis - completely unselfishly.
When someone drops a five into the offering plate, completely unknown to anyone around them and never taken off of their taxes and never spoken of again, that's altruism.
When someone lets in a car when it's not their turn, but it's clear there's a good reason that person needs in, that's altruism.
There are beyond millions of examples every day.
In the grand scheme of things, your point is valid as a generality. In the meat of day-to-day life, on a personal level, altruistic tendencies abound.