The argument here, I think, is going in the wrong direction. Defining a language as a "secret language" is not judgmental, Lorcan, so I don't think it's an example of prejudice. I think we're proceeding from a fundamentally faulty idea of what a secret language actually is, because the questions of whether Shelta is literally a secret and whether it is a "secret language" are different questions. English-speaking Children use pig Latin, (at-whay id-day, i-ay, ay-say?) egg-language (weggat deggid eggi seggay?) , ubbie-dubbie (whubat dubit ubi subay?), etc., as "secret languages," but it is easy enough to learn them, and many children will teach you if you ask them. They are not languages that ARE secrets, but rather languages that are FOR secrets. (To clarify this, think of a secret language as a language for communicating secrets, not as a language that is itself a secret...)

Lorcan's example of the people in the shop is a good one. Those people presumably often speak those languages among themselves when no one else is present to be excluded. So while such a language can function as a secret language in some situations, it is not primarily a secret language. My grandparents used Yiddish as a secret language, to keep stuff from my parents. But this does not mean that Yiddish is primarily a secret language, because they also spoke it in other contexts.

Secret languages are languages (in fact, many are really not full languages at all but more like codes) that you learn so that you can keep secrets from other people in given situations. So the question is: do people normally speak Shelta, or do they speak it primarily when they wish to exclude an outsider? If it's commonly spoken, I think most linguists/folklorists would say it is a living language that can sometimes function as a secret language. If it is used primarily to exclude people not "in the know" then it is primarily a secret language. Again, this is not a question of judging the travellers, just a technical question about Shelta.