Maybe you need to specify in the original post more clearly. Ask people to stay within X conversation and not to deviate from it. "This is about X, please withhold all comments about Y."
However, with things like suggestions there is a lot of spillover effect into other things.. changing/implementing one thing can have really great or really horrible effects on other things. Newtons third law: For every action there is an equal and opposite reaction.
or am I off-topic talking about physics?