If ambulances use the HOR exit that's one thing. But if not, I'd still prefer to live with very minor inconvenience than the threat of a 40mph wrong-way-down-a-one-way-street dgaf nutter. With the best enforcement in the world (which isn't likely to be delivered on any consistent basis) you still can't rule this out. With a row of steel bollards you can.
This type of intervention is already in place in the wider area (the east end of Stanstead Road and Spring Hill/Peak Hill in Sydenham are two examples), and is being rolled out widely by some of the more progressive boroughs in London, such as Hackney and Camden.