On average, each teaches three courses, with each course meeting three times a week. A research university has even greater intensity since it must be competitive with the world's best researchers. Otherwise it won't attract or keep tenured faculty, federal grants, and foundation support. Universities should grant tenure if that faculty member is the best obtainable in a nationwide search. That individual then makes a commitment to the institution.
Tenure protects independent work.
The faculty member can, without fear, begin research that takes four or five years to show results. It's hard to get new ideas accepted. Albert Einstein, when he tried to have his first papers published, could only find one journal that would publish them. We've got to support brilliant people. Tenured faculty must produce enough to fulfill their responsibilities.