Payroll and benefits are complex and hard to administer. Complying with overtime and income tax rules across jurisdictions alone make outsourcing payroll and benefits a sensible decision for many organizations.
The problem isn’t outsourcing a difficult and error-prone requirement that is never part of the core business (payroll and benefits). The problem is those outsourcing companies selling that data or using it for purposes other than managing payroll and benefits. Unfortunately we live in a world where anything we participate in, voluntarily or otherwise, potentially exposes us to data harvesting and our information sold to the highest bidder.