There might be one case somewhere that could be found where a firm that technically counts as PE isn't shady but in general the very idea of private equity is shady so it follows that all the PE firms would be shady also.

The point of PE isn't to run sustainable businesses that provide quality products and services for customers while treating their employees well. The point is to rapidly suck all the value out of businesses by loading them up with debt, breaking laws, mistreating customers, and exploiting employees. What happens to the carcass of the business or to the customers and employees whose lives have been destroyed doesn't matter to them.