Objectivism and Critical Rationalism present reasonable targets for criticism. The main content was developed by a single person who took responsibility for creating something reasonably well-defined and complete. This is typical of original work: a pioneer comes up with some new ideas, develops them, names them, and they mean something.
Libertarianism and Inductivism are difficult to criticize because they mean different things to different people. They are full of internal debates. The terms don't identify any particular system of ideas. Instead, the terms broadly refer to many different thinkers and ideas with some similarities – and also plenty of differences. Because of the failure of these terms to unambiguously identify any particular ideas, debate and progress are more difficult. (Sometimes ideas start out this way. Other times they start with a specific meaning and become vague as a defense mechanism because criticism refutes the original meaning.)
Some philosophical positions begin with a clear meaning, which can then be discussed. Others begin with group similarity between multiple inadequate ideas (or, worse, people) and then stay vague forever.
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