You can request it - yet you cannot control it - but a request is different to a demand. Requests are questioning - demands are statements.
(sorry - word nazi here[;)])
The most gracious thing to do is just move on. Why even bother reading or responding to people who you feel are destroying your thread? You are perpetuating the behaviour by paying attention and making what is perceived as a demand, over and over. (Like I say - it is a perception - I am only trying to discuss with you how it comes across to others).
In the way I have been taught - these are my traditions. Passed down by Dominants and alpha submissive men and women through many years. If I am at a munch, holding a discussion and it spins off the topic I began, then let it. Those people who are swirling off that which I want to find out about, will continue with their little side conversation and the main one continues. If it is bothering the conversation, then my traditional training points me to either take that person aside politely and ask them not to disrupt if they would be so kind. Not 'please stay on topic' which is a command. If someone shows me disrespect by diverting the topic I have started - should I disrespect them in the same manner? No - because my tradition, my training is to be a light in His eyes, to pay Him honour and be an example of good training by respecting myself, and above anything else and anyone else, by respecting Master and Masters House. My tradition and training dictates that is rude to disrespect anyone, even if they disrespect me - and discounts any knowledge that person may have. It means I learn that little bit less and those watching the example one is setting, even less.
Peace and Rapture