If you're referring to HN policy then for an established account it's not really shadowbanning, because dang will tell you that you're banned and why. Being treated as a useless noob until proven otherwise is being treated as an adult.

Twitter is different (although perhaps more different than it needs to be). Seeing as you ask, here is how to handle content deletion on Twitter without infantilizing users.

Don't ask a user to "delete" a tweet – something which has no effect on that tweet's visibility anyway. Just hide it and tell him why. If the user chooses to appeal, that appeal can go forward without restricting the use of the account. Give time-outs sparingly. They should be more of a final warning than a routine measure. If it's necessary to give a time-out, start the clock immediately, not when the user takes some action.