You can't be "left alone" in a society that provides basic needs for the most unfortunate - disabled, sick, old, homeless, etc. because it takes money to pay for those things. If those needs are left up to charitable donations, like you would like, it ensures at least some of those needs go unmet. I'm unwilling to accept, as an individual in the wealthiest society the Earth has ever produced, that any of those needs go unmet. This is why libertarianism will never work in a society where individuals do not feel direct kinship to fellow citizens. Some people do, but most people don't, and there are even those among us who actively despise anyone different.
If taxes are "theft", then failing to provide those needs when you have the ability to, but choose not to is "murder"