Well, I'm no economist...
The knock against deflation I've heard discussed most often is that purchases get delayed if everyone knows prices are dropping (why buy for $10 dollars now what you can get for 8 bucks tomorrow?)...so prices drop more, and purchases get pushed back yet again...on and on, prices dropping and no one buying. Flow of money grinds down, and we know where that leads.
If you have money, you're laughing. If you don't, opportunities to scare some up become fewer.
I'm not making any claims about the veracity of the argument.