Comparing murder to antitrust therefore seems to be a pretty weak argument. Deontological libertarians would view the use of force required to enforce antitrust as authoritarian overreach. They would see no moral justification in the enforcement of arbitrary limitations on the voluntary transactions of consenting parties. They would see these as tyrannical.
This stems from a core disagreement about the nature of society. Some people see it a as a collective project for the good of all participants (the sticky points being the definition of "good", and the non-optionality of "collective"). Others see it as simply an agreement to coexist peacefully and cooperate only voluntarily, while embracing the Darwinian nature of said coexistence.
Each side is well meaning I'm sure, but I find it hard to reconcile these two worldviews.