There can be many reasons why people hate Bitcoin. The most general one is that it's something relatively new and risky, and it's a part of human nature to be cautious and a little hostile to new things because if we don't know it, it might be dangerous. Another reason is shilling for something else: Bitcoin is a scam, but _____coin is revolutionary / stock market is awesome / investing in property is great. And, of course, there are reasons mentioned here before, such as people with negative experience who invested and then sold at a low price point or got scammed or people who're jealous and greedy.