Unfortunately, by walking away you do open yourself to ongoing asset recovery action. Some years down the road, when big box bank sells the right to collect this asset to 'Knee Break Asset Recovery" and KBAR renews this right (in Florida this can continue for 17 years) you can find yourself in real prolonged financial purgatory. This is serious. KBAR can get you fired and make you unemployable.
There is good news. Your underwater amount is not insurmountable. Contact a real estate professional who specializes in distressed property and alternative financing. Do not contact a real estate agent who specializes in selling bank owned homes. You have real options of which you are unaware.
Walking away is the option many have chosen. One must believe the banks, from the great good will in their hearts, will ignore the revenue available by assigning collection rights. It's a bet based on wishful thinking.
Be aware, only Tom and Tammy taxpayer is encumbered with moral or ethical responsibilities. The bank can and does to what ever they will, legal, illegal, immoral, unethical and downright evil. Don't be persuaded by such arguments. It is a business decision. Consult an attorney or financial adviser to understand the possible consequences to you.
You will find very little justification for placing yourself in such great peril over a $12K difference. It is likely you will discover you are actually at a break even situation.
Consult with your attorney or financial adviser and real estate professional and set the course most beneficial to you.
Best of success.