I think it basically comes down to this: Once the left establishes an institution and populates that institution with its kind, the institution can never be diminished in the slightest - let alone dismantled - because that represents a setback for the left's march toward the power to engineer the entire social and economic order. That will not do.
Think about the way they look at public schools, which are heavily staffed by unionized teachers who always toe the Democrat line: If anyone chooses to pull their children out in favor of another option, the left goes bananas because they say it weakens the public schools. And it's not just private or religious schools. Even charter schools, which are public but don't necessarily play by the left's rules, are a constant target for their ire. It's always the good of the institution that's paramount to the left, not whether the people are really being served by it.