Manners are about not making other people feel uncomfortable. The rules of manners are voluntary and negotiated -- maybe you want to make someone feel uncomfortable. Sometimes it might be impossible to avoid making one person uncomfortable without making another person uncomfortable.
There is a trend in political correctness aim to replace voluntary manners with power.
A transexual might make the novel claim that it is bad manners to call a male-to-female transexual "he". Someone who disagrees may refuse. Both parties are free to disassociate from the other. (What if they are not free to disassociate, for example colleagues? Whose rule of manners should be followed? The socially normal one, of course, whichever that is.)
What if someone claims it is bad manners not to remember to use her bizarre pronouns (per, em, xyr, vis)? Clearly this is not reasonable disagreement, but an attempt to impose claims about manners as an exercise of power. The sole purpose of the novel claim about manners is to exercise power.
One could publicly campaign to try to make one's novel claim about manners considered the default, correct choice, in a dispute between colleagues mediated by a Human Resources department. This is the politicisation of manners.
One strategy is to enlist the power of the law: to make it illegal not to obey bizarre whims about pronouns. This is the legalisation of manners: to make what was previously the voluntarily negotiated norms of human interaction, a matter for the law.
It is good manners to refer to a male-to-female transexual as "she", even though "she" is not really a woman. Good manners does not require "she" should be allowed to compete in female sporting events.