If the courses are run specifically for a group of people, based on their attributes, this subjects them to bias before they even walk in the door.
One way that this sort of sexist/racist approach could be detrimental is if it's served by one, or few, organisations, the courses could accidentally (or, in extremis, purposefully) be using methods that cause entrenchment of existing partitions between different groups of people. Perhaps one set of courses teaches in a certain innocent manner, and the minorities that consume the course therefore learn in a particular way, or leave out key issues.
There's also the possibility of being indoctrinated against those groups that are not welcomed; again, not necessarily on purpose - I don't intend to demonise such organisations.
Somewhat analogous to recent machine learning/algorithms being found to be prejudiced as their programmers may be unknowingly prejudiced - e.g. facial recognition working poorly for faces of people with dark skin.
