He did not just admit it, he went a step further saying :
-- I will be the face of BPD --
No other celebrity has admitted it before, and I do not blame them. It is not a requirement to go public about serious private struggles. Even with friends and family, it is not always easy, and sometimes not a good idea at all to expose all that. Sometimes it is better to keep this between you and your doctor. It's a choice.
You know what ? I don't think it's fair to say : 'oh, Angelina Jolie should admit, when is she going to talk?' It's her life , her choice. And maybe she does not even have BPD.... I guess she does, but can't be sure. It's not a requirement for her to admit this kind of stuff in public.
To come back to Brandon Marshall , Yes, thank you man ! Not just because you admitted it , but because you offered to be the face of BPD.
We know that many celebrities came forward to talk about all kinds of disorders and mental illnesses, but not BPD.... So, Marshall gave it his face !

Not bad, right ? Handsome+sexy, talented, respected, and loved by how many fans around the world ?