There are all kinds of myth-memes about dreams in the media...
Spoiler Alert: The movie Inception is one of the more recent culprits responsible for disseminating misconceptions about dreaming into the popular culture. Ideas with no factual basis - even about the mind in general - have hooked on to the public imagination and maintained their own belief for years. For instance, you still here people say "we only use 10% of our brains." This nonsense has been around since ancient times, long before anyone could have known something like this. Today, we understand that the entire brain is always active, with different regions being more or less noisy depending on what tasks are being performed. But, if the whole thing, or any one brain region, were too active, we would have a seizure. Sure, some people's brains may work better than others at this or that task, but the point is that certain statistics and facts are completely made up. Some claims may even sound good, but upon a closer look, are made out of thin air.
Back to movie-implanted misconceptions on dreaming. (For a description of actual dream theories, click here.) There was a movie back in 1984 called Dreamscape, which used the idea of shared dreaming - multiple people being in the same exact dream. Before stating why I do not think this possible, I have to say that anything is possible: the best math and physics guys and ladies say that it is more likely than not that there are a huge number of parallel universes, each with their own rules and versions of reality. OK. With that said, I have never, nor has anyone credible I've ever heard from, reported repeatable, verifiable, magic. And sharing dreams would fall into the magic category. It would be a simple matter to scientifically test the ability of shared dreaming. Hasn't been done. Yet, shared dreaming is such an attractive idea that maybe people assume it is possible, or maybe even regular. The idea has been further solidified in movies such as The Cell, and of course, Inception. I actually know of a way to share information between a dreamer and the outside world, or even between dreamers in real time, but we are talking about a tiny amount of information exchange being transferred with the help of technology.
Warped time in dreams in relation to the "outside" world is another common misconception about dreaming. People believe this one as if it is a scientifically accepted fact that everyone knows. Not at all true. This myth was popularized a long time ago but has no good evidence behind it. You can have a dream of a false awakening, but you can't dilate time by digging into deeper dream strata. Dream time is the same as dream time, maybe even a tiny bit quicker. This can be studied, has been studied, and the results are clear. You cannot gain years of extra life by going deeper and deeper into dream layers, a la Inception. And another thing: You cannot add otherwise "lost" time to your life by becoming lucid during what would otherwise be regular dreams. First of all, you only dream for at most a few hours per night, and nobody is going to develop their lucidity to a point where they are nearly always lucid during dreams for the rest of their life. Lucid dreaming is fun, but it can be exhausting. You probably wouldn't always want to be that "on" while dreaming.
Another fairly popular idea is that lucid dreaming is dangerous. This one is kind of like "if you die in a dream, you'll die for real." If the statement were true, it would still fail a basic scientific principle: falsifiability. There would be no way to know if people were dieing in their dreams, because they would be too dead to tell us. Except this isn't true, and people do "die" in their dreams, with no actual harm to their physical body. The premise behind this myth is that in dreams we work things out and disrupting this process is dangerous for our psychological well-being. No evidence for this. Most theories of dream function do not match well with the evidence accumulated in the many thousands of dream studies conducted over the past century. Likewise, most of these theories supported one or another version of dream-as-problem-solver, and the only "problem" that dreaming seems to address is the problem of feeling calm and at ease. It solves that for us by making us more vigilant, i.e., paranoid and on defense. Lucid dreaming may actually be healthy for us because in them we can choose to act bravely in the face of threats.
Another accusation I could see would be that lucid dreaming is used as a form of escapism from reality. Maybe for some, but I doubt this is common. First, achieving lucidity is not easy for most people. Even though Galantamine may be helpful for well informed lucid dreamers, the whole affair is not as simple as popping a few pills. Inducing lucidity usually requires a well-functioning, goal directed mind-set, and a willingness to tackle obstacles head on. And lucid dreaming may not be dangerous, but lucid dreams can be macabre or scary, just like regular dreams often are. This reminds me of how only a few people choose to repeatedly experiment with strong psychedelic drugs. The psychedelic trance is an extremely interesting experience to have, but far too taxing - like a trillion megaton awe bomb - for daily, or yearly, use. Lucid dreaming is not quite as shocking as a powerful entheogen, but your respect for its tone will develop if you get to spend some time in that mental space. I want to emphasize that the sometimes threatening air in lucid dreams are merely there because the dream system is biased to be like. It is not really a personal thing, we are all built with similar dream architecture in our brains.