It is wrong because hedonism is usually tied to individualism, and a individual pursuit of happiness, that sometimes might work in short term, or for one generation or two, but end always results in problems for the collectivity that make everyone LESS happy.
The current way of life, hoardings things, "stuff", without a purpose or objective, wanting to be in the "haves" just to not be a "have not", agressively wanting more money aiming just to pleasure yourself or be more happy, only results in people, inadvertently or not, taking things from others that needed them.
Many societies with far less money and technology were happier, because what make people happy is a question of how they are spending their time.
If you work 70 hours a week for a very long time, to buy things that make you happy, you are wasting your time, you won't get happy this way, and might make others unhappy, starting with people close to you, like abandoned family or significant other, or children, to people that you hurt without even knowing, when for example in your own pursuit for happiness you do things without noticing how evil they are, like working for a cigarrete factory for example.
The most happy societies were ones that people worked 40 hours a week, period, no more chores, if the men were working 40 hours outside home, women worked 40 inside home, but both worked 40 hours, nothing more, our society people started to take increasingly burdens pursuing more money, and don't noticed that most people now work way more than 40 hours, and have long commuting times, and have few time to do what they enjoy, or to improve themselves and others.
My uncle once told me, that he noticed how pointless it was how much he was working, when he finally could buy a big TV and a PS3 (those are absurdly expensive here in Brazil, and people have much less income too, so they are absolute luxuries) and noticed he did not had time to enjoy it, he bought his dream videogame, and his dream game (Gran Turismo 5), and just could not play it, then he realized, what was the point?
Hedonism isn't about hoarding stuff. Working more hours to buy more stuff is the opposite of hedonism. Contemporary hedonism implies something like partying at Ibiza 24/7, but the original meaning was more like the enlightened dad spending more time at home cooking organic meals for his family.
