I think you've got it right, for the most part, in that the internet has changed the way people look at things. Not just BDSM, but nearly all aspects of life. Doctors these days often complain about people who watch House or read WedMD and think that makes them a medical expert. Or people who watch home renovation shows, and think that makes them a skilled enough to start tearing down walls in their house.
These days, it's so easy to get a ton of information on whatever you're into, that the question of whether or not it's GOOD information isn't often raised. The Old Guard system can seem antiquated, and worse, slow! Having to learn thing a bit at a time, having to listen and get the approval of others? Pff, I can read 50 Shades and be just follow that!
As for what you say about people not thinking the lifestyle was about sex ... maybe we've had different experiences! A staggering number of people I've met (mostly outside the Library) think BDSM is about nothing BUT sex! hehe .. buttsex .. Sorry, sorry, got distracted by juvenile humor again. Where was I ... oh yes! A lot of people seem to think the kink and 'dressing' of BDSM is just about getting their gender specific bits off. About getting to the climax. Which although enjoyable .. is well down on my list of 'most important and enjoyable things in a D/s relationship'.
And I think that's why I like the Old Guard system! If you go into BDSM with the end goal of just having sex, can you really understand it the same way someone who actually studied and learned from a greater community might? The mental and emotional part has to be at least as important as the physical, or (to me) it's just vanilla sex with weirder toys.
How to get more people coming into BDSM to take it slow and look at the Old Guard system, rather than jumping in genitals first and thinking they know everything just from easily digestible media ... I have no idea. Offering cookies maybe?