Never let it be said that I don't give all the facts - or opinions, be they mine or other people's - at my disposal. I have always erred on the side of caution when talking about Goth subculture (which, as you may have noticed, is a subject that comes up quite a lot...) to avoid offending anyone, or frightening babybats and the parents of babybats. But, as many commentors have pointed out, this counterculture is not one hundred per cent sweetness and light - there are bad apples in EVERY social group or community, and Goth culture has its flaws and downsides just like any other. I thought I'd bite the bullet and try and highlight some of these, whilst providing my own, hopefully-not-too-inaccurate opinions on why I think these behaviours might occur (and of course, comments are open for you to add your own two cents).
Maybe the person, band or behaviour they are referring to is NOT Really Goth, in which case other Goths are likely to agree (for example, most Goths will agree that the band Slipknot - whether or not any given Goth LIKES their music, I happen to - are not Goth) and they will not be thought of as being elitist for making such a statement. But if they are calling someone or something who is generally accepted as Goth, not a real Goth (are you with me?) they will be referred to as 'Gother than thou' or 'elitist'.
And whilst most of us tend to complain about this behaviour and attempt to invalidate it, as I am doing now, in many ways the majority of us are guilty of elitism in some small way. If you've ever rolled your eyes at someone in a Marilyn Manson T-shirt, muttered about the person wearing blue jeans at the spooky club, or looked at someone's preferred list of bands online and decided they're not a 'real Goth', you've done it too.
I personally like to think that this admittedly silly behaviour stems from wanting to defend the subculture that most of us feel very strongly about. If, for example, you see the bully from high school clad in black and sporting a pentacle necklace, your likely first reaction may be to assert that they are 'probably not a REAL Goth, anyway', because you don't want this person associated with the culture that you so love.
I suspect that many of us hold strong ideals about the subculture, and we tend to start rolling our eyes and mumbling 'not really Goth' when we are confronted with something or someone that doesn't fit well with our own idea of 'how Goth should be'. To use another example, many of us are nervous about hipster Goth, because we are worried that some who are interested in this style are exploiting our dear subculture as just another trend. So a lot of people slam all hipster Goths and the entire associated fashion as 'not REAL Goth', which isn't really fair on hipster Goths who genuinely love the subculture, the music and the aesthetic and are simply celebrating it in a manner that THEY prefer.
Or, when confronted with a mallgoth type in badly-applied make-up and baggy clothes, we are uncomfortably reminded of our own early years, and try to prove to ourselves that we've moved beyond such by deriding (usually mentally, thankfully, since most Goths are not actually bad sorts!) the poor misguided creature as 'not a real Goth'.
What I'm trying to say is that this tendency towards elitism does not actually always mean that a Goth, whether they have made a single comment or are well-known for having a 'Considerably more Goth than thou' reputation, is unkind or unfriendly. They may simply be feeling defensive or threatened about the subculture and/or their place in it, and their defensive behaviour and comments translate as elitism to the bemused witnesses and irritated innocent on the receiving end. So if you are ever 'treated' to this behaviour, just ignore it, because it probably means that in some way or another the person is intimidated by you.