If we can distinguish "progressive" and "regressive" ideas through reason, that can only happen with an open discussion that gives both sides' advocates equal,

If we can distinguish "progressive" and "regressive" ideas through reason, that can only happen with an open discussion that gives both sides' advocates equal, fair treatment. If an idea is universally considered regressive, then usually it doesn't come up. Ideas that people are discussing are usually ones where it's not completely clear yet, to everyone, whether it is a good idea or not. In that case, allowing both sides fair advocacy is critical to making a fair decision.