When I read "pseudo-Russian" I thought this was about learners making fools of themselves using slang words they don't master...

Slang is always an addition to any language. It is not poorer. It's not as if speakers of slang are unable to understand the standard language, even if they don't comfortably use it. But actually they do use it if the need arises.

I think if a native speaker explains or uses slang terms, then he or she should simply clarify that they might be fit only for certain purposes. I am in practically daily correspondence with several native speakers of Russian, and most of them, if slang or colloquial terms arise, say "don't say that in front of your boss" or "you wouldn't say that in the presence of minors or women". And clearly the opinions about individual words differ. For example, one lady correspondent happily used "покеда" to say bye bye, while another said "that's a bad slang word from a criminal context, don't use it". Both, by the way, being language teachers.

I have picked up colloquial terms from Russian and even Ukrainian, and from (classical) literature as a learner you may easily pick up outdated terms, too. As a learner you may be unable to assess the value of an expression (little use in using дякую instead of спасибо if the correspondent isn't Ukrainian), but it is still necessary to acknowledge the fact that different levels of speech exist in any language and to come to terms with them.

Subcultures will always have their specific terms and expressions, and learners won't always come into contact only with mainstream culture. Heck, maybe they even want to come into contact with specific subcultures! And it even extends to pronunciation. I mean, which textbook prepares you for що instead of что? There really is no use in concentrating only on standard literary language. It is the common denominator on which to base one's studies, but sooner or later one has to progress to non-standard variants. It is up to native speakers helping us learners to mark specific variants as such, and that should be all. Separate sections do not help because the learner doesn't know what goes where in the first place.