I've seen this phrase a couple of times recently. Come to think of it I've heard it or something very like it ever since I've been on the kink scene.
Sometimes they mean it to be that they're worried about some kind of influx of people who are experimenters. (People who've just read 50 shades of grey are the new worrying barbarians at the gate apparently.)
But are they? No they don't know about anything much to do with kink and they've had their interest piqued by some not very good pulp fiction. So what? Nobody entered the kink scene complete with an encyclopaedic knowledge of every technique safety issue, protocol or whatever. Nobody did.
So why were you not a disaster and this next person surely must be? Life's a learning process for us all. (Yes not absolutely everyone, we all know people who never really learn but you get the point.)
Personally I don't think the barbarians are at the gate. Some people will come look and walk away again. Some I think will really have found something that makes a difference to their lives.
Is that bad? Does it matter if someone got to something that they really love from reading badly written pulp fantasy like 50 shades of grey, the story of O or having seen a girl tied to the railtracks in an old black and white movie?
What matters is that they have a chance to find something that's great for them, that brings them pleasure and ultimately isn't that what the whole thing's about?