That's quite an edit you made to your question! You are basically asking:
I borrowed money. I can afford to pay it all back, but should I?
Why wouldn't you pay it all back? The concept of debt settlement, as well as other types of loan forgiveness, all revolve around a basic assumption that at the time of purchase, you had both the means and intention to pay off the entire loan in the future. But despite your best intentions, at some time later your circumstances changed such that you could no longer afford the payments. Settlements are not intended to be used by people that don't need to settle. If you can pay, you absolutely should. It's simply unethical otherwise.
That being said, there are some unethical people that could afford to pay off the debt but choose not to so they can save some money. The system is designed to prevent those people from doing it again (at least in the near future) by reducing their credit score. So, you can try to settle if you really want to, but it'll hurt your credit for up to 7 years.
Regarding the legitimacy of debt settlement companies, they basically work by charging you to negotiate on your behalf. For example, if you owe $10K, the company may negotiate $5K with your bank and charge you $6500 to pay off the debt. The reason these companies are considered scams is that they oftentimes try to convince people to settle on debts that they don't need to settle. Also, note you can't usually negotiate a settlement with a bank until after you stop making payments for at least 3 months. The reason for this is the bank wants to see you take a hit to your credit score first so they know you're serious about actually needing to settle.
Conclusion: don't ever settle your debts if you don't have to.