Why do liberals want billionaires (who've worked all their life to earn their fortune) to give away money?

Because no amount of honest work makes you a billionnaire.

Screwing people (clients, personnel, taxpayers) over is the only way to become a billionnaire - except for simply inheriting it

Many of the billionaires want to give away money, and I don't see why we should stop them.

If you're talking about taxes, the billionaires would have been able to earn their fortunes without taxes.

 No.

They don’t want the billionaires to “give it away”

Democrats want to seize it from them at gunpoint.

Why do billionaire like Bill Gates and Warren Buffet state that they feel they do not pay enough taxes?

The left is a culture of envy. It poisons their world view. All their economic models are based on envy. They believe zero sum game economics, and Keynesian models of government economic adjustments. They believe. Bastiat's "Broken Window Fallacy." In short, the only way they could be so colossally lacking in economic wisdom, is to believe the alluring nonsense told by leftist academics. Your average small business owner could teach economics far better than the supercilious clowns in academia. It's why A.O.C. (the Econ grad in the squad) sounds so stupid to normal people. She is full of envy, and believes lies.  

Where did you get that BS?  Liberals want billionaires to give away money.

They want no one rich. That basically means the American dream, being able to achieve a life of any level you wish with no one bothering you, coveting what you have like an aszhole, or shoving their nose in your business, is impossible. 

You see, if no one can be successful, there really isn't much point in saving up money or trying to build a future for your family and children, or anything. There's no point in trying to achieve something great in your life, because selfish aszholes, like communist left wingers, will come along and covet your schit and steal it from you. In the mind of a covetous aszhole, it doesn't matter if the money was earned fairly. They still have theft and jealousy in their heart. 

Because a capitalist economy is like a pyramid, and when the top has it all they give it to their kids.

You just said it, you used the word work.  It's an alien term to the left and they will not stand for it!