> treating their citizens like adults
For most society level problems we are OK as long as most people behave responsibly most of the time, so this approach is great. We can inform our citizens and they can enforce good behaviour amongst themselves by tutting and grumbling in a disapproving way.
This is not true of a contagion. Occasional "just this once won't hurt" violations are enough to break containment.
That's why the countries that enforced strict measures early — suspending individual freedoms — have had better outcomes for their health and economy.
Fighting a contagion is like hygeine in a kitchen. You know which surfaces and utensils are clean or dirty, and you don't put the dirty things back with the clean things until they've been cleaned and dried.
In the same way, you try to establish regions where a contagion is/may exist/is not, and then expand the clean regions. If people have their inalienable human rights, then you can't do the basic containment strategy, because your clean regions keep getting contaminated.