Expressing concern over deflation (i.e. the inflation rate turning negative) is the way in which people tell you that they have no clue about economics and just repeat what they heard others say. The inflation indexes we use are an aggregation of millions of different price changes. There is a substantial amount of dispersion around the overall inflation number. This means that when the inflation rate is near zero, there are many goods and services whose prices are already falling.
This means that the WSJ discussion of the risks of deflation in the euro zone is rather silly. It tells readers:
"Mr. Draghi said Saturday that he sees no evidence of a broad-based decline in consumer prices, known as deflation, and that there is no sign people are delaying spending in hopes that prices will fall."
With the euro zone inflation rate at 0.5 percent there are undoubtedly large numbers of goods and services for which prices are declining now. (People may not recognize these price declines since the inflation data use quality adjusted prices. This means that if the price of a computer increases by 5 percent, but its measured rate of quality improvement is 10 percent, then the government statistics will show a 5 percent decline in prices.) If the rate of inflation were to turn negative and become deflation, it simply means that the percentage of items with falling prices has increased.
While a lower inflation rate is worse than a higher inflation rate in the context of a badly depressed economy (it raises real interest rates and makes wage and price adjustments more difficult), there is no consequence to crossing zero. People who understand economics know that deflation doesn't matter. People who whine about deflation are trying to tell you they don't understand economics.