Aside from the concern about enforcement difficulties there is also the concern that it is basically an empty pledge not to do something that the other side has at points and may very well continue to do so, with or without this.
If peaceful coexistance is the desired object that that would be best handled through a treaty negotiated by the relevant officials for both parties and then submitted to the Senate for ratification. Of course that resolves the point about reciprocity, but not the enforcement problem.
Yes, that would require amending the crime bill. Although in the future we may think of something like the RL Logan Act.
