I love DLs, but you need to learn to do them properly. You can herniate a disc brushing your teeth.
What DLs do as a side effect is teach people how to pick up things properly. Most people are too tight in the their ankles, hips, and rest of their posterior chain so they are picking things up incorrectly all day long. This sets them up for injury. Learning to DL properly is a great way to teach how to properly pick thing up, and I agree it will likely help with most people's back pain. But, doing anything improperly can cause injury.
What DLs do as a side effect is teach people how to pick up things properly. Most people are too tight in the their ankles, hips, and rest of their posterior chain so they are picking things up incorrectly all day long. This sets them up for injury. Learning to DL properly is a great way to teach how to properly pick thing up, and I agree it will likely help with most people's back pain. But, doing anything improperly can cause injury.