There are so many PE firms with such different practices that's it's difficult to make any generalized case for or against them. Ideally they provide liquidity for small business owners who want to sell and move on but lack other buyers. PE firms also do rescue many businesses that would have otherwise failed due to incompetent management or lack of capital: the mainstream press loves to hype up failures and abuses but seldom reports on successes.

Defined benefit pension plans shouldn't be a thing in the first place: they're too risky for workers, employers, and taxpayers alike. All pensions should be replaced with defined contribution plans like 401(k) where assets are safely held in individual named accounts.