You can actually do much worse than a public defender. Calling e.g. a lawyer who works for a "mill" (like those guys who advertise on TV, in my hometown it's Kerry Steigerwalt -- who makes a living pleading out DUI's with the least amount of effort possible, but would take your murder case without asking) will get you a guy who is just as overworked and understaffed as the PD, but unlike the PD, does not care about justice at all, only making money. They will do anything that results in a reduction in their workload, even if it means years in prison for you.

At least with the public defender's office you get someone who gives a shit, even if they are overworked.