Everywhere I've looked and everyone I've talked to says 당신 is a really rude word for anyone outside of loved ones like husband/wife, please remove this.
For anyone else coming here, I'd like to summarize the podcast's relevant points.
When used in direct conversation, it's considered lowly, foreign, or tantamount to 'fighting words'. It is more about just addressing someone without much regard or, at the least, improperly with respect to your relationship, as far as I can tell.
You can, however, use it for translation purposes, for when you require indicating the "you" in the sentence. This comes up in the spoken form when you switch the topic of the sentence and need to directly refer to "you". So in other words there is a specific, but practical use there.
A third use is in writing and music. Music is not directed at anyone, thus saying 당신 is totally fine, encouraged, even, it seems, given how frequent it is. For writing, I understand it as how any language is more specific and more formal when written (99% of the time, anyway), so that would explain why it is allowed.
Another use is between two intimate parties (spouses was the specific example), but it was given with the caveat that it is mostly used by middle-aged and older, giving me the impression that it is a bit more antiquated and proper, but even then it is sort of rare and not incredibly common among all people.
Finally, you can use it as a form of an honorific to refer to someone respectfully in the form of he/she when someone is not there.
So it seems the biggest takeaway here is formality, and context. Use it in the right context, or when writing or translating, use it for your spouse, but don't use it with just anyone, and for those cases, default to 너 if you actually need the pronoun.
Hope this helps!
To be a little more clear it can be rude but honestly it's not used a ton.
I don't think you should censor knowledge, just put the (very informal) caveat. Besides, it's completely fine to use with those close to you. It'd be weird to treat friends like the equivalent to "sir".
Uh. Either everyone you know is crazy or you're lying. 당신 is uncommon because mostly foreigners use it, being habituated to pronouns.