The reason Social Security, Medicare and Medicaid spending is so high is because of out of control health care costs. What the government does with those programs is agree to pay for health insurance and other benefits. But what it doesn't do is establish what those benefits should cost. That part is still left up to private enterprise, and whatever price is set must be paid.
Cutting back on the benefits themselves would help reduce the deficit, sure. But the better goal is reducing the price tag of the benefits (by allowing Medicare part D to negotiate for better drug prices, for example).
Why is that the better goal, you ask? Think about Social Security and Medicare for a second. These are programs for the elderly, who are now retired, and who have spent their entire lives paying into these programs. Their money, out of their paycheck, every two weeks. This is not an entitlement, it's a promise, a good that's been paid for. How can you morally justify turning to these people and telling them that the benefits they paid for and were promised are going to be cut?
There ARE other options. We just don't pursue them because we're too afraid of ruffling the feathers of health care companies.
The Constitution mandates that the full faith and credit of the United States must be maintained, so I'm not sure how the debt limit even works legally. $16 trillion is a huge number but it's also an arbitrary number. If you don't understand why the US Government failing to pay it's obligations is bad then frankly... that's on you.16 trillion in debt is dumb.
Think about what would happen if you told your credit card company that you had exceeded some arbitrary level of spending for the year and weren't going to pay your bill until you decided for yourself whether that level of spending versus income was acceptable. Try it some time and see how it works out.