What should a Billionaire give?

The age old question, what is the value of human life, or can a value even be put on the life of a human being? According to the passage by Peter Singer, there are many billionaires who give lots of money to various charities just to share their wealth and shoe that they care. I on the other hand think that some of these billionaires give the money so it will look good on themselves or companies, or to get hefty tax ride offs. When I read this passage, I get a strong vibe that Singer himself is a pholathropist who believes that billionaires should give away much of their wealth. Again, I think that billionaires, for the most part worked for their riches and should have an option to give or not, therefor not making it an obligation. Singer also states in the passage that the wealthy should give a higher percentage of their wealth that those less fortunate. I disagree with him again here because then you are putting price tags on people and taking away their freedoms and rights as americans. If a wealthy person wants to give away lots of their money, then thats great, but if not, they shouldnt be obligated, or even expected too. Its solely their choice.