Well, I agree with you, but it's clear to me that currently the legislature gets more scrutiny in elections than judges do. So not only is the legislature more responsive to the people than the judiciary, but under the constitution, it's the legislature that writes the laws, not the judges. For better or worse, the minimum sentences have been properly legislated, and we do not want judges overturning proper legislation and mandating their own law without a proper legal cause.
If you think the law is too strict, take it up with the legislature. But don't give the judges the ability to overturn every law that they happen to think is unwise. Overturn "unconstitutional" absolutely, but "unwise" is so subjective, that you will cede all legislative power to the whims of the judiciary, and that destroys the checks and balances.
I didn't say that a judge should overturn a mandatory minimum sentence.
What I said is that they are poorly conceived, written, and reactionary, and that offend people's sense of justice and foster disrespect for the law.
Furthermore, since most judges are elected. Your point that the legislature is more responsive only reinforces my position, that people are too lazy to discharge their civic duty to pick fair ones and voting out morons.