The moment you post something it's placed on Steem (not Steemit, that's just one way to read Steem), which is the blockchain and backbone of Steemit.
The way a blockchain works is that once something is placed on the blockchain, it cannot be deleted. Allowing to delete something would break the chain, causing all sort of unpredictable behavior.

So no, there will never be a "Delete" button, you either think hard before posting something or you can later edit it and remove the content.
In the latter it is still possible to retrieve the original message by traversing the blockchain.