Liberals view special interests as exogenous to the policy process. You have to overcome special interests to create good policy. Libertarians see special interests as endogenous. Policy is what creates them.and,
Most important, liberals will always say that we need government involvement in food policy, energy policy, education policy, health policy, etc. When they observe that a particular policy serves only special interests, they may appear to side with libertarians by supporting a rollback of the offending program. However, while the libertarian will put forth the notions that public policy is often self-defeating and that it is impossible for policy to be immaculately removed from special interests, the liberal is never going to concede those points.