"Insinuating"? You just assume, without justification, that he's making those judgements at a distance and doesn't know those people personally. You've got the argument backwards: he's not claiming that everyone with "unconventional style" has low self-esteem and is looking for attention. He's observing that attention-seeking people with low self-esteem do flashy things to get attention.

I know a goth girl (real goth not poser goth, for those who care) and she told me that she dresses defensively because she gets bullied a lot. That's not an assumption or judgement by me, that's what she told me. I also know a former Wiccan girl from a broken home, and a satanist who has anger management issues and a drug problem. That does not generalize to all goth/Wiccan/satanist people but that doesn't mean it never happens.

May do flashy things to get attention, and that's not even positive attention as evidenced by this post, so at the end of the day they must do it for themselves because it'd be easier not to do it at all. I don't know what makes someone a 'poser' and someone 'legit'; what legitimizes their existence isn't appearance, what they practice or what they've been through. It's still a blanket statement of assumptions that doesn't need to be perpetuated.