The Posse Comitatus Act is a good and wise law. However, the laws can only be as good/bad as the persons charged with enforcing them.
In the case of the Waco massacre, the executive branch of government in charge of enforcing Posse Comitatus became the violators. We have a constitutional mechanism for dealing with this situtation and it is called impeachment. The congress and Senate failed to do their duty by letting clinton cop a plea for perjury. Then they failed to convict.
This is why character matters and a Westly Clark presidency with the fithly clintons running the democrap party would be disasterous for America.