An obligation is an action one owes one or more other people. When one fulfills an obligation one does something good but not all good actions are obligations. Some actions are supererogatory, they go above and beyond obligation. I am obliged to pay taxes but I am not obliged to donate money to charity. Both actions are good but the latter is a supererogatory action.
The moral status of an action depends on whether the action is an obligation. Failure to perform an obligatory action is wrong. The value of an action does not so depend. An action can be good even if it is not obligatory. It is good to give a present to someone; it is not an obligation.
Some obligations are performed willingly, others not. If one does not desire to perform a supererogatory action and does not perform it, then one has committed no wrong. If one does not desire to perform an obligatory action, and does not perform it, then one commits a wrongful omission. If you don't pay your taxes, then you receive punishment.
Strictly speaking, 'payment' and 'gift' are similarly defined. To pay something to someone is to fulfill an obligation to fulfill a debt or promise to another person. People owe money to their bank and pay money to fulfill the debt. In contrast, people give money to charity. They do so even though they do not owe anything to the charity.
Consequently, taxes are not gifts to the state. Rather, taxes are payments to the state. Giving is a supererogatory action. Payment of taxes is an obligatory action and, therefore, not an act of giving. Being motived to give without obligation is a good thing. But it does not matter whether or not one wishes to pay taxes - the taxes must be paid anyway!
If someone says that to oppose the raising of taxes demonstrates a lack of compassion, they are confused about what taxes are and what gifts are. Taxes no more demonstrate the compassion of the one paying than the curliness of one's hair demonstrates the power of the brain that lies beneath.
Indeed, since people express compassion by giving, we can generally assume that if giving is high, then compassion is high. Not so with taxes. How high a tax is cannot reveal the compassion of the heart of the people paying tax. In fact, giving is generally higher in countries with less tax partly because people have the money to give, but also because they are highly motivated to take responsibility for looking after one another. I once visited a YMCA in a country with a 60% tax rate. No one from that country worked at the Y. I was told that the reason they did not do so was because they expected the state to do so ('why else am I paying all these taxes?').