Something being ethically bad is insufficient to rule it out. The degree of the ethical failure matters, as does the purpose of the action.
This will inevitably be read to imply I'm advocating Torture which I am not. I'm merely pointing out that binary ethical/unethical is insufficient.
Oftentimes in the US it is less about a busy defense attourney and more about the prosecution offering a plea deal to skip trial. I can't say with any certainty why this is done but I believe it's due to overcrowding in courts and jails.
Many attourneys will suggest the defendant accept the plea deal because it's a sure thing. It's a lighter sentence than if the defendant went to court and when a case goes to court -- especially a jury trial -- it is impossible to say how it will turn out and it could end up far worse for the defendant when compared to the plea deal.