Taxes versus Philantropy
When rich people claim that philantropy is better than taxation, their argument is essentially that their causes are more worthy and/or that they can manage them better than governments. They are putting themselves over governments. These are the arguments of kings. Sure, there may be some benevolent ones, but history has proven that they more often than not invest in causes that are more important to them, their family, and their friends, and not the needs of the pauper.
It's sure nice that some bazillionaires donate to worthy causes like eradicating tuberculosis, measels or cancer, but if we hauled in more tax money, we as a society could invest more in those efforts as well.
Let them blow their money on rockets and flying taxis, and donate to issues they believe in, but only after proper taxation.