For the last time -
Hard Brexit = out of the single market and customs union.
Labour policy = out of the single market and customs union.
I'll leave it at that because it's a basic fact that you seemingly won't accept so any further discussion is pointless.
Labour want closer ties with the EU. In 2016 Corbyn was as much a part of the problem as all the other hard Brexiters.
The Tories would drum up all sorts of nutters that voted for Brexit by re-making it as a political hot potato.
In your view, would it be better for Labour to be 100% honest and possibly leave the Tories in power for the next 14 years? What would happen with the EU then? I can guarantee absolutely that under the Tories, the Brexit would get harder and include stuff like leaving more stuff and more rights being stuffed - Human Rights is the tip of the Iceberg. Just look at what shitheads like Truss and Frottage have been up to recently.
And there are still plenty of dickheads in this country that believe they were right who would turn against Labour again in a heartbeat if Labour pledged to tell everyone in the world that these dickheads are fucking stupid - which would be what they would be voting on should Labour announce a full reversal.