Why is it okay to discriminate against men but not against others?

Here are three scenarios:

1.) A privately owned club provides women with free entry and open bar on Friday nights.

2.) A privately owned club provides access to only Caucasians on Friday night.

3.) A new privately owned club provides African Americans with free entry and open bar on Friday nights.

Here is my question: why is it legal to discriminate against men but it is not legal to discriminate against Caucasians, African Americans, or other religious groups?

How does civil law protect privately owned businesses? Also, how does civil law protect the freedom of association for private business owners? We can have women only gyms but there are no Caucasian only athletic centers.

Exercise centers such as Curves is open only to women but if Curves changed their policy and only provided membership to any one minority or racial group, the ACLU would be all over the center.

When does freedom of association come into play?
Thank you for your answers.

Freedom of association doesn't come into play until some form of government attempts to curb that right. The Bill of Rights does not apply to private actors, except in a couple very fact-specific situations.

As for scenario 1, they do this for the benefit of men; without such an enticement, there would be tons of guys and no girls.

As for scenario 2, most likely federal law would apply because pretty much any business today has interstate connections through running its business (i.e. cups made two states over and transported to the club, etc.). Congress has passed laws banning illegal discrimination against minorities under its Interstate Commerce powers in the 14th Amendment. Those laws originally were aimed at things like hotels and restaurants that refused to serve blacks, but they would today also apply to your fictional club.
Of course, the difference between the scenarios is that only the second one is a complete bar to certain groups, where the other two merely place a hurdle for certain groups (cover charge) while giving a free benefit to another group (free booze). I believe only this scenario would be totally illegal.

Also, you must remember that discrimination is denial of a right. Charging some groups a cover and not others is not a denial of a right, but the granting of a benefit. The same goes with free drinks. The club has the right to charge women for the drinks, but it chooses not to. This is not discrimination, but rather it is selectively choosing who to give a free benefit to. As for Curves, they probably have argued that some women strongly desire a place to work out where men aren't ogling them, and where the gym is aimed at their specific needs. I don't know if anyone has ever challenged them on it, but I am sure they would win. And no, the ACLU would not be all over that place because the ACLU is only worried about individuals' rights under the Bill of Rights, and (as I said earlier) for all practicable purposes the Bill of Rights does not apply to private actors, only government actions.