Earlier quoted context omitted.
Of course - if governments could raise funds by donations they would not tax. I hate taxes, but I hate the absence of taxes more :)
Are you saying that if there are more effective ways of raising money, governments necessarily know about them? I'm on your side with regards to taxing, but governments are slow-moving beasts that are often controlled by ideological moves rather than practical ones.
http://www.fms.treas.gov/faq/moretopics_gifts.html
They obviously don't take in anything more than a trivial amount of money. If you think that people would donate an equivalent amount of money if their taxes were eliminated - then you must have an awful lot of faith in people's inherent generosity in the face of their own self-interest. The economically optimal decision for any one person is to not give, but in the aggregate that means we don't have funding for infrastructure, research, etc.