When Britney was melting down she always struck me as stubbornly determined to self-destruct whilst railing against oppressive management and years of being 'Disney's Pop Princess'. Whether something similar, i.e. frustration at the demands of the record company (how many dates is his tour again?) is beginning to affect Bieber or whether he's just a knob is presently unclear.
It certainly looks like, aside from anything else he's getting into, Bieber has a monstrous ego and a massive sense of entitlement to behave as he wishes with no regard for others. Of course when you have a phalanx of record company lackeys just creaming themselves to pander to your every wish so as to keep the gravy train rolling, it is hardly any wonder.
Apropos of Britney I've always suspected a certain strength of character and "bloody-mindedness" in her that whilst it initially led her down a dark path and into mental health issues also (with the help of the conservatorship) enabled her to climb back out of the abyss afterwards, something that not all of Showbiz' "lost sheep" have been able to achieve (I'm looking at you Lindsay!)
Of preference, I'd rather Bieber was just an arrogant, bratty little child "acting out" than someone in the grip of psychological turmoil (and ideally neither!) as most people grow out of the former but the latter cannot always be left behind.