How might a liberal have to respond to the suggestion that some workers might prefer to work at highly routine, unchallenging, and boring jobs?

Employers have no obligation to eliminate these jobs.

These jobs do not necessarily suppress the human faculties of rational and autonomous choice.

While it may be true, on the one hand, that as long as no one is forcing employees to do these jobs, employers don't have to eliminate them, it is also true that accepting the ethical legitimacy of these jobs violates the fundamental values of rational and free choice.

Employers have no choice but to eliminate these jobs.