There are massive layoffs planned in oil producing states. Major decreases in expected state tax revenues. Real estate prices in Texas are already falling.

A lot of the recovery following this past recession was attributed to the energy industry. A big fall in oil prices could unravel that progress.

It's short sighted to say high prices => bad, low prices=> good (unless you want to score cheap political points). There are lots of intermediating effects, so the overall impact is difficult to discern.