People on the left are those who, looking at any human society, with its inevitable stratifications by power and wealth, think things would be better if more of the power and wealth available were redirected toward the bottom of the heap. But the redirection of relative opportunities to the less advantaged is the distinguishing feature of the left. Conservatives believe that any such attempt to redirect opportunity, power or wealth would make society function worse and should be avoided. Reactionaries persuade themselves that society would function better if more advantage were given to the relatively well off. Left and right, as thereby defined, are not normative terms.
Capitalism is a system that works via self-interest.
The powerful, but also the gifted and the fortunate, tend to win at the expense of the weak, but also the stupid, feckless or unlucky. A society that allows the results to become cumulative and lead to savage inequalities is one danger but another is a system that stifles enterprise or even self-reliance by too procrustean an attempt to redistribute the results of economic activity. That definition of left and right does not encapsulate all of politics. Evidently there are many issues, such as the reform of institutions, political freedoms, the environment, educational methods and, perhaps, gender issues, which can divide people on other than a left-right basis. An important instance is the issue of communitarian values versus permissive or libertarian ones in matters such as drugs legislation and in the framing of social policy.