marley didn't get suspended for not wearing the sea shell bra. She got suspended for not following the assignment. Marley could've easily worn a different gaga costume (and lets be real, there are so many gaga outfits out there, and she did say to Jake she was fine wearing a bra made out of gloves or something so obv she must be somewhat comfortable with wearing something revealing SO WHY DIDN'T SHE WEAR THAT OUTFIT INSTEAD???)... Marley could've chosen any costume - she was not forced to wear the shell bikini, she just had to wear a Gaga costume.
And the fact that she went against the assignment to prove a 'personal agenda' was part of the reason she got suspended 'I'm not going to change who I am for any performance or any GUY' shows that Marley is making a statement that she is who she is and if a guy doesn't like that then get over it. She dressed at Katy Perry to send a message to Jake that she is who she is.
Not to mention the assignment was to 'get out of your comfort zone' - her going around and prancing around like Katy was rude because everyone else was uncomfortable with how they looked as Gaga, but there Marley was as Katy, and in her comfort zone. If she really did have a problem with wearing the bikini then she should have said something about it to Sam, and have her wear a different Gaga outfit. And Sam was only angry at her so much because HE was doing the performance for his personal agenda, and trying to impress Penny - obviously Marley coming out like that ruined it for him (yes he over reacted)
Marley got suspended for not following the assignment, not for not wearing a seashell bikini (Glee is a comedy, obviously the line was put in to create humor. If it was any other costume then yea, it wouldn't be a big issue because it's not sexualized like the bikini - it's just seen as disgusting because the fandom is so uptight about everything) - Just like in the purple piano project how Santana got suspended for "setting the piano on fire". She didn't get suspended for setting the piano on fire, she got suspended because she wasn't being a team player. Look at this from an actual assignment point of view (as in a hand in on paper). If you don't do the assignment you get punished. Say this is in a PE class, and you have to do an assignment on herpes or something where you have to look up diseased genitalia. If you don't hand the assignment in because 'you are not comfortable with looking at pictured of ****s and vaginas' obviously you're going to get in **** because you didn't do the assignment when everyone else had to. If you felt uncomfortable, speak to your teacher about it. They'd come up with alternatives to it and then you wouldn't have to do something you're not comfortable doing.
That said though, Marley was treated like ****, and I think it's stupid because Will is all like 'omg we only got X weeks until Nationals we gotta rehearse" LIKE YEAH YOU REALLY DID YOURSELF GOOD THERE BY KICKING SOMEONE OUT OF THE CLUB FOR A WEEK.