That's very true.
They've already 3D cameras on the market, so I'd imagine that by the time these 3D TVs become widespread, 3D camcorders will in turn become widespread also and I'm sure there's little stopping a pirate popping a pair of 3D glasses on their 3D camcorder.
Then again, even today, no matter how well a pirate succeeds in illegally recording at the cinema, there is simply no replacement to going out to the pictures, just like heading out for a meal. You wouldn't say to your partner "No, we'll eat at home instead". It's hard to replace the experience of gong to the cinema, unless of course the locally run cinema is in an awful state.
Of course if the cinema goes to the stage of running airport style security (which some do to confiscate hidden snacks & drinks), then I can see what puts some off going out to the pictures.