Also, in the end, it is but fashion, clothes, and yes, while our subculture means a lot to us, and the hypocrisy of those who would mock us with one hand and then take their styling tips from us with the other is galling, it does not do any material harm - it is not the same as say, throwing stones at someone or denying someone a job because of their subcultural affiliation. There needs to be some level of perspective. The mainstream fashion industry commercialising our fashion and aesthetic does not stop us from enjoying our own subculture, it does in no way prevent us from still seeing a Bauhaus t-shirt as a way to appreciate the band or from studding our leather jackets ourselves, it just blurs the significance of things to those on the outside.
I would not judge someone else on what they are wearing, nor presume them to have any of the above motivations on the sole basis of their clothes. That is just as silly as assuming that all Goths look the way we do to actively rebel. I would also not tell anyone what they can and cannot wear. If you live in a country where there are no laws restricting your fashion choices, then you are free to wear what you like, and the same freedom that allows Goths to wear Goth clothes extends to non-Goths wearing Goth clothes.
As always, I recommend never approaching others with pre-concieved notions of what they might be like before knowing them, and being polite even with those whom you disagree with, and that extends to people who are wearing your favourite band t-shirt but don't know who, say, Siouxsie and the Banshees, actually are.