Well, in short, by definition it spreads misinformation. Even if a particular propaganda message is technically truthful, by design the message has been alerted to focus on certain things while obscuring others. In other words, it's not only inherently subjective, but it's designed to be misinterpreted as objective.

Finally, I do not support any of the common causes or ideas that propaganda is usually intended to reinforce (e.g. patriotism sounds harmless, even positive, but largely is used to encourage bigotry and xenophobia).

What's wrong with propaganda? Everything.