1) in an economic downturn, one would expect charitable givings to decrease due to economic contraction. I think the evidence from the 2008 recession is somewhat mixed on this topic. Most governments, not reliant on personal donations, do not face the same sort of budget issues (which is another debate).
2) Charities have the ability to discriminate. They can choose how to allocate donations in ways that can include or exclude certain segments. This is in some respects true as well for government spending, but once again boils down to the allocation problem.
3) economies of scale. Larger organizations are often less redundant than a group of smaller organizations, reducing overhead.
> My belief is that forcing somebody to do anything against their will is inherently immoral. Taxation is included in that. It's not that simple of course- it's all relative, and sometimes taxation can do enough good to outweigh that morality.
Since you are not fully opposed to taxation, would you accept a taxation scheme for a government program if an independent and well researched study showed that government spend outperformed private programs by 2.5x, 10x, etc.? Or is it more that any issue that could be addressed via private charitable organizations should be off-limits for the government?