@Elmud,
If you were to try to have a conversation with me in person and I did not know you well, you would find I have little to say. Even with people I do know well, I find it difficult to get a word in when the group consists of three or more. I am least silent when I am conversing with only one additional person.
I don't have any particular reasons for being a generally silent person. It simply seems to be the way I am wired. But I find that my silence contributes to excellent listening skills, and I have a received a fair number of compliments on my quality as a listener.
If there is a reason other than natural personality for my silence, you might think of my discovery that arguing does little to nothing to change the mind of someone else who disagrees. There was a time when I felt I needed to make my beliefs known to more of an extent than I do now, but that was before I realized that other people have their own beliefs, and it is unlikely they plan to exchange them.
So I would suggest that when the topic of discussion is an issue that your discussion mate disagrees with you on and is under no circumstances going to change her mind, that is the time to be silent. Even if she might change her mind, you could find that it is ethically difficult to attempt to force a change of view, depending on what the issue is.
If you are conversing with people who feel as you do about the topic, that would be the time to enjoy a discussion that lasts well into the early morning hours if need be.
But of course I am someone who frowns on conflict, and someone else who does not mind it will probably disagree with me. Understandably, he and I would avoid the topic of conflict in a discussion we might have.