Like most attorneys, I believe everyone who is accused of a crime should have legal counsel. The public defender system is designed to provide legal counsel to persons charged with crimes who cannot afford an attorney. Unfortunately, the demands on the public defender system means it cannot really meet that goal. This system has to keep the income requirements for a public defender extremely low due to the shear number of people seeking a public defender. Unfortunately, this means a significant number of people do not qualify for a public defender due to their income, but have no ability to pay for an attorney.
If you have the resources to obtain a private attorney, then you should not be putting more strain on an already overtaxed public defender's system just because you could qualify due to your own income and are not required to disclose your other resources. Doing so would be akin to eating at a homeless shelter because the food is free, or getting money from a welfare program even though you have adequate financial support. You are taking away services from someone who really needs it.
The moral reasons for not getting a public defender rather than a private attorney unfortunately are not foremost on most people's minds when they are facing criminal charges, which is why most attorneys don't mention it. Attorneys may tell you their experience, skills, and the time they put into your case is why you should hire them over a public defender, and those reasons may be perfectly valid, but you should also consider the ethical issues of overburdening a system that is meant to help people who otherwise have no choice but to face the system without counsel.
Attorneys such as myself try to keep our rates low so we can help to close the gap caused by the stress on the public defender's system. But the fact is there are still many people who don't qualify for a public defender and can't afford a low-cost attorney. These are the people who are hurt the worst by those who get a public defender but could have paid for a private attorney.
So, in short, if you can ask the question "should I get a public defender or a private attorney?", you should get private attorney.