I don't want to donate to charity through my employer
What's keeping you from wanting to donate?
I don't trust them to spend my donation wisely
I think that's a reasonable take.  If you're giving money to an organization, you have the right to want to know what that money will be used for.  Try and find a better organization to donate to!
I don't think there's any point. I'm sure they're all inefficient at best, and many are outright scams.
It's true some are, but you can find good charities to support. There are objective websites that rank charities by how efficient they are and how much good they do. Also, at a local level, you can often find food banks and others that provide a lot of help for your community, which you can discover by talking to your friends and neighbors.