While many Marvel Comics fans may look at Captain America as the beacon of truth and justice shining brightly across the entire fictional universe, it seems he’s not as pure as everyone gives him credit for–something that is proven true with his one R-rated rule for joining the Avengers.
Steve Rogers was chosen to become Captain America, not because of his physical appearance or ability, but because of his spirit and the fact that he was truly a hero at heart. After receiving the experimental treatment that turned Steve Rogers into a Super Soldier, his heroism only became more pronounced as he was finally able to make a real difference in the world. While Cap’s first duty was fighting the Nazis in World War II, he would later join the Avengers and battle a plethora of villains who didn't only pose a threat to this planet, but sometimes even the entire galaxy. However, it was during his time with the Avengers that Cap’s unwavering incorruptibility was called into question.
Captain America Tells the Avengers to NOT ‘Get Together’ with Supervillains
In Ant-Man: Last Days by Nick Spencer and Ramon Rosanas, fans are shown how Scott Lang spent the last days of his life before the armageddon-level event that happened during 2015’s Secret Wars where two Earths crashed into each other. For the most part, it’s spent as any fan of Scott Lang’s Ant-Man would assume: a little heist-action, some superhero-ing, and even a bit of personal fun with a consenting partner. Basically, Ant-Man got laid, and by doing so, Scott broke one of Captain America’s most important rules for Avengers members: don’t sleep with supervillains. Scott hooked up with the villain Beetle aka Janice Lincoln, but before he decided to do so, he remembered that Captain America told him never to sleep with villains upon his first day as an honorary Avenger–which actually calls into question a very important point: why did Captain America have that rule to begin with?
In the past, Captain America has been no saint when it comes to upholding this particular rule of maintaining one’s moral high ground as an Avenger. Steve Rogers has romantically tangled with a member of the Serpent Society, Diamondback aka Rachel Leighton, even though she was clearly a villain who supported the efforts of her evil group. While Steve was able to find some level of redemption for Rachel (which resulted in her own team trying to kill her), it is clear that he felt burned by the experience, and made a vow that he nor any other Avengers member would go through that again.
While the motives behind Captain America’s rule aren’t confirmed (with his experience with Diamondback simply being the most likely reason), it is easy to see how the rule itself is decidedly R-rated. Superheroes discussing who they can and can’t have sexual intercourse with–especially when it’s about the villains they’re supposed to be fighting–probably isn't going to appear in the overwhelmingly family-friendly landscape of the MCU any time soon. For this reason, Captain America’s one rule for joining the Avengers is a bit too mature for modern-day Marvel movies, and the fact that the rule exists at all proves that even Captain America isn’t exactly the boy scout fans originally thought.