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I wouldn't say Steem as a whole discourages it rather its the few very powerful vigilantes that are enforcing a certain structure for sharing articles. Its an often debated subject on what the "rules" are.

Would I be able to submit my own content I've already written on other websites without getting penalized?

If you can prove its yours then you won't be flagged. I have many articles I brought over from an older blog. They made me put a link on the blog to verify it was mine.