What Is ‘Sexism’?

A remarkable entry from Merriam Webster’s dictionary (which I found linked from the Wikipedia article):

sex·ism noun \ˈsek-ˌsi-zəm\

1 : prejudice or discrimination based on sex; especially : discrimination against women

2 : behavior, conditions, or attitudes that foster stereotypes of social roles based on sex

The first definition has been in use for a long time, and is (I would suggest) widely recognized. But note the second one. According to Merriam Webster, any expressed positive view whatsoever, however limited, of any historically-recognised (a.k.a. ‘stereotypical’) gender-based social roles is, by definition, sexist.

Have I understood that correctly?