Wages tend to be sticky. That is, they adjust slower than many other prices. This works against workers in an inflationary environment and for them in a deflationary environment. Keynesian monetary stimulus is premised on the "sticky wage" theory, basically the idea that by printing money you can reduce workers' real wages in the short run and increase the output of firms.
Of course the flip side is that if workers' real wages increase too much in a deflationary environment, this could lead to high unemployment in the short term.
Sharp deflation, like during the Great Depression, is bad as you say. Slow deflation, like the period after resumption, is not bad.
In reality, the economy is quite capable of coping with any mild change in prices, and quite bad at dealing with sharp changes in price. It doesn't particularly matter whether those changes are up or down.
Of course the flip side is that if workers' real wages increase too much in a deflationary environment, this could lead to high unemployment in the short term.