Recently I asked a question and then based on one of the answers I got, proposed a solution to the question I asked. At which point I was told that "original research" was out of scope for the Philosophy SE. At which point does speculation about a question constitute just that, and at which point does it become original research?
To my mind there should be zero "debate" conducted on the main page, which is not intended to host discussion or conversation.
If you are trying to start a debate, discussion or even informal conversation about some point that is being raised, it may help to keep in mind that this is much closer to the intended use of the chat space.
If you are able to specify a bit more about the particular details of the problem you're encountering it may be possible to be a bit more specific.
In general I'd just gently remind community members that questions on the mainpage are not prompts to open general discussion. Any "speculation" you are tempted to embark upon should therefore be sharply focused around elucidating specific philosophical works and excerpts. Citations should be provided where possible to help ground commentary in terms of very particular contexts.