The ethics can be a grey area for sure, but it really depends on the intentions of the person behind it. If someone buys something, then tells others to buy it, people will say that he's talking up his own book. If he doesn't buy it, then tells others to buy it, then people will say that he doesn't really believe it. In the end we have to look at the arguments behind what people are saying, to find out if they're trying to manipulate us or the market, as their actions won't necessarily tell us the full story.