There is ZERO credibility that this development will be used to "create a countermeasure", especially mrdeepfakes is a key communication channel there.
I'm not talking special to mrdeepfake.
My argument still makes a point that you can't just forbid it. Someone else will do it anyway
Of course you can, even if somebody else does it. Case in point: any penal code.
How can you force stopping development of software?
One of the more egregious examples: https://www.wired.com/2011/03/aleynikov-sentencing/
This also leads potentially to more or better image/video signing Technologie.
And yes just because someone develops this in the open doesn't mean that someone else is not developing it in parallel but hidden.