I don't see the problem with deflation. It allows one to save their money and get good future value for their saved money. I think inflation is wrong. Inflation depletes your savings.
Deflation encourages hoarding and reduces the velocity of money - why invest money with risk when i can just hold onto it and increase it's value.
In a deflationary money system, the more people that horde the greater the value of the currency. It's like a catch-22, the more you save the more that people want to save.
Instantly all of people's discretionary spending grinds to a halt and businesses can't get loans because they have to spend a currency that will return in smaller amounts (because everyone else's money will be worth more) and have to pay it back in larger amounts that they may never get. Additionally, if you buy X amount of stock and tomorrow the currency is worth X * 0.9 you have lost money before you started. If it takes you 6 months to get the stock from wholesaler to customer you may never be able to sell it for more than what you paid for it. May as well just keep the money in the bank at 0% interest.
Large amounts of inflation are bad because people can't spend money fast enough for it to be useful, but deflation is worse because it literally stops the economy dead in it's tracks. This is why central banks keep inflation at around 3%, it's not enough to affect day to day prices so business and consumers can plan their budgets but it is enough that people don't keep money under their mattresses. Even putting your cash in an interest bearing account is in everyone's interest because that interest is you being paid to lend your money to businesses or other people to keep the flow of capital going.
People who say deflation is bad should go find a local community college and take Economics 101, it will teach you the basics theories of how this stuff works.