In Punch Out!! Wii, Princess Peach was considered for the secret boss character in Exhibition Mode and Last Stand Mode. However, she was scrapped in favor of Donkey Kong because the creators felt it wouldn't be right to "hit women" and that it would "send the wrong message." I don't agree with their statements and feel that Peach should have been in the game. I can list several good reasons why this is so.
-The surprise factor
Most of the opponents in Punch Out!! are very well-built and pose a threat, especially in Title Defense onwards. Even Glass Joe, the boxer with a win-loss record of 1-99 managed to subvert players' expectations. Peach would have also surprised players by being more than just a "helpless, distressed princess" that they see in her home series; If the Witch from Left 4 Dead is able to be more threatening than the Tank, who's to say that Peach wouldn't be more lethal than Mr. Sandman?
-Peach has power!
Just like Death Battle stated, Peach is very athletic and has played many sports to justify her strength and skill. The Olympic games even had BOXING where she is playable. By excluding her from Punch Out!! Wii, that's like saying she is weak when other games have proven otherwise.
Ironically, Little Mac was included in the latest Smash Bros game as a newcomer; there, he can fight Peach with little to no complaints. If Nintendo knew that the bruiser from the Bronx was going to be part of the roster, then it wouldn't be so bad to add Peach if Little Mac were to fight her anyway. Even more ironic considering that they added Little Mac, the guy they didn't want to hit women, in Smash 4, which has more female characters than the rest of the series combined (including the extra skins like Robin, Corrin, Villager, Wendy, and Wii Fit Trainer), and many of them have cute, anime-esque designs.
-There's no holding back in competitive sports
Since when has a real competitor ever held back on account of who or what someone is? A sensible person would know that going easy on an opponent would only result in having their ass handed to them. That's something that I don't think a lot of people get, unless of course the opponent in question is evil, a jerkass, or an evil jerkass. Peach is kind and sweet, but just because someone is kind and sweet it doesn't mean they're not going to be an aggressor. Beware the nice ones.
-Punch Out's Positive Use of Stereotypes
Punch Out!! Wii is considered to be very tasteful in using stereotypes in a way that enhances a character's personality instead of degrading them. As stated in Gaijin Goomba's "Is Punch Out Racist?" video, this is a major step-up from the previous Punch Out entries in the days of Pizza Pasta, Vodka Drunkenski, and babbling Piston Honda. I believe that it could also be applied to gender (and any other category) if Peach were included in Punch Out!! Wii; just because she is very pinky and girly, it doesn't mean that she is soft and weak. You don't have to sacrifice beauty/niceness for strength, or vice versa.
-One Rule: Boxing Gloves
There are so many boxers in Punch Out that use unfair tactics which will never fly in an official league (location varies). Great Tiger has magic, Soda Popinski heals himself during every intermission while you can only do it once, and Aran Ryan headbutts and uses a weapon. Peach has unconventional combat tactics that I think would fit really well in Punch Out!!, many of them pulled from Smash and the Mario sports games: Toad for counters and company (like Bear Hugger), magic (like Great Tiger), self-healing peaches (like Soda Popinski's soda), fast footwork (like Disco Kid/Kid Quick), and frying pan/golf club/tennis racket weapons (like Title Defense!Aran Ryan). For Peach's own things, her Peach Bomber, airy/floaty movement, and trollish taunting ("Did I win?").
Overall, the decision to exclude Peach from Punch Out!! Wii comes across as misguided at best and hypocritical at worst. I'm sure that there were good intentions, but they did not think this through. Not adding Peach because "it's wrong to hit girls" makes her look unable to dish out and take pain like a champ, while Little Mac would look biased for not having problems hitting people unless they're female. Nobody in-universe makes note of boxer X "being a credit to his race", and this would apply for if nobody called Peach good "for a girl".
Peach and Punch Out!! belong to Nintendo.
"Oh, did I win?/This is fun!/Peachy!"
"The winner is... Peach!"