Advertising gives the impression, especially to children, that they can and should have everything they want. This makes people too interested in material things. People are becoming more selfish and obsessed with their possessions, and losing their values of patience, hard work, moderation and the importance of non-material things like family and friends. This harm their relationships and their personal development, which has serious effects for society as a whole.
Our society is build around the idea that companies produce things that people want, and this is what makes us prosperous. If consumers suddenly stopped wanting to buy so many products then what happens to the people whose job it is to make them? The economy will suffer terribly. Of course some people take materialism too far, but most people buy just what they need and then a little extra when they treat themselves. This is a much better situation than one in which people can only afford to buy the things they need - that would be a step backwards.