The left -- Robespierre, Marx, Lenin -- wasn't always pacifistic, tolerant, non-hierarchical and humane. The right -- Bismarck, Hindenburg, Ludendorff -- wasn't always free market and individualistic.
The left of a century or two ago could be very bloodthirsty and intolerant. The European right of past centuries could be statist, hierarchical, and controlling.
Mussolini came out of the socialist movement. There was much about him that was left. But he organized his fascist movement specifically to combat socialism and Communism and allied himself with property owners, so the movement had a serious right-wing component.
Today's liberals and conservatives correspond to the liberal/conservative center of a century ago which was very weak in some countries and viewed with contempt by many in the Interwar period.
Without control is there really ownership? And is there really any capitalism when the state controls everything it does not own?
The fact that Mussolini fought other socialist and communist to protect businesses his Fascist party controlled no more stopped him from being a socialist than Stalin killing Trotsky and other communist he saw as threats to his power stopped him from being a socialist/communist.
Actually, they were always like that. Just ask antifa or various other left-wing groups (not to mention Robespierre and Marx either had destroyed the hierarchy or otherwise had an explicit desire to see the state fade away).