How to Win on Progressive Causes
Maha at Mahablog has written extensively and wisely on the subject. Here's one of Maha's careful but blunt comments that comes right to the point as about clearly as one can:
Years ago I formulated a basic rule for successful demonstrating that I call the “Bigger Asshole” rule. The job of public protesters is not to change the minds of the powerful people they are opposing, but to gain public sympathy for their cause. Especially in politics, the powerful won’t change until they are compelled to do so by a sufficient critical mass of public opinion saying they must.
Maha elaborates further in the comment section of her post:
This is the whole point of the Bigger Asshole rule. You are not trying to change the minds of people you directly oppose. You are trying to win everybody else to sympathize with you more than with the people you oppose. Public support and sympathy give you some leverage to actually change things. Not having it means you are whistling in the wind.
Years ago, I talked about a related issue concerning what I called persuadables, the small but important percentage of people who are actually willing to listen. But Maha's point is a larger one involving a much larger group. One way to look at it is that when you argue with an opponent, you need to remember who the real audience is: the people who are looking over your shoulder and are listening in. How you conduct yourself is as important as what you say (as an example, you don't put up with bullying, but you work hard to make sure you don't become a bully yourself).