Copy-and-paste, "Give me a tutorial or complete example"
These users don't seem to understand simple coding tasks like conditionals, loops, and, well, plain old logic. They don't seem to understand what they are doing, and why the code they're "writing" works (or breaks). As a result, they come off as either new coders, lazy coders, or coders that are entirely over their head and lost. These are not students, and their tasks are not homework.
They seem to operate via copy-and-paste. They need hand-holding tutorials with plenty of example code in order to perform their tasks, because everything they do is based entirely off of that example code. "Tutorial or complete example" is effectively a code word for "give me the codes."
The questions are usually complex, multi-step odysseys that are hard to actually accomplish. They usually arrive in the form of "How do I write this complete application? Please send me a tutorial or complete example." When asked to show their progress so far, they are frequently unable to do so, usually again insisting that they need an example/tutorial.
While there is nothing wrong with asking for or providing example code, the frequently broad nature of the user's questions makes them extremely difficult to answer. Pointing the user to the documentation, even when the documentation contains examples is ineffective for various reasons.
While I'm not sure that I'd classify this type of user as a "parasite," the low-quality nature of their questions causes many of them to be closed or downvoted, though this rarely serves as an effective deterrent. (Further, it seems that the worse the spelling and grammar, the faster the close. I'm not going there.)
The "require minimum reputation" proposal would impact these users directly, as they rarely earn upvotes and almost never answer other questions.
The "cap rep from questions" proposal would not impact these users as frequently, as most of them don't seem to be in it for the rep, and would take a very, very long time to reach a sane cap given their low-quality, downvote-ridden questions.
Further, outside of more aggressive closing and downvoting of this type of question, I'm not sure that there can be any deterrent. These users either do not want to learn, or are unable to learn. Manuals are useless. Links to reference material are futile efforts.