Earlier quoted context omitted.
Do you allow people to conspire to commit crimes? Yes, that's exactly what you do. I would much rather we let a few (more) crimes get through here and there. Weakening privacy for everyone isn't worth it.
You'll find the people value security more than privacy. This is why conspiracy to commit crime is already illegal. That's just how society is. Your choice on whether you want to live with the rest of society or not.
Just making conspiracy illegal doesn't mean you don't value privacy; it depends on what means are permissible to obtain evidence for the conspiracy.