The powers that be already try to say no to jury nullification by doing the following:

• Failing to tell people that they have the right to vote not guilty no matter what the facts are
• Using jury selection questions(er, tampering) to exclude anyone they think might nullify

It doesn't really matter whether or not it is made illegal though. As long as we have trial by jury (usually avoided by using trumped up charges and offering plea deals these days) every thinking man and woman who sits on a jury has within their power the ability to say not guilty and stick to it.

This is a right not because someone says so. It is a right because as long as a unanimous vote is required by a jury it only takes one man or woman to say not guilty and refuse to say otherwise.

No one can make you say guilty.