The biggest reasons for always virtualizing are around hardware abstraction and free. Virtualization is free and easy, which is important as it takes away the "why not virtualize" caveats. Virtualization has, effectively, no downsides. It actually lowers the cost and effort of systems administration and through the miracles of abstraction it actually makes the overall system simpler, rather than more complex!
The hardware abstraction aspect is critical because it makes our systems more stable, rather than less stable, and more flexible for whatever we might need in the future. It reduces technical debt with no real cost of its own. These aspects mean equal or lower cost with lower risk.
It's these aspects, the "always pros" and the "lack of cons" that puts virtualization into the solid "always category.