The issue in that example is with witness tampering/coercion/bribery. You’re entering a third factor into the mix that has nothing to do with the argument at hand. This isn’t a critique it’s a red herring.

The argument is that false rape allegations do huge amounts of damage, both to the accused and to those who make truthful allegations. Perpetrators should therefore be adequately punished.

If someone makes a allegation of rape, and during the legal process the accused commits further crimes in order to affect the outcome of the case, that is a separate, criminal issue. It is serious but it has nothing to do with the above argument. That is why you were downvoted to oblivion, poor argumentation.