A homeschooling co-op is literally us just reinventing the wheel. A large enough co-op becomes a school system and a school system eventually adopts a standard curriculum.
People who do co-ops might not object to public schooling in principle but to the particular implementation that their locality has adopted. If co-ops becomes public schools with better management, all the better.
And if they become public schools with worse management and driven by crazy people.. what then?
Straw man, slippery slope, false dilemma, causal fallacy.. do they teach rhetoric and Aristotelian logic in public schools?