Here’s the problem with the Pence rule: if women represent 10% of your workforce, or if they represent 4% of your leadership, men only hanging out with men ostracizes the women.
Heck, I’m a dude, and when I was going through a hard time and was in no position whatsoever to socialize with the boss, my colleague: Mr P — invited the boss to cookouts at his place, socialized with the boss without inviting others — and Mr P got promoted.
Same thing is true for the history of guys being guys and going to the golf course and not inviting women — amazing amount of bonding and actual behind-the-scenes business takes place in these settings.
Leaving women out leaves them out of the ability to grow in the business.