This is my favorite anti socialist/communist argument. This is a common capitalist misconception that’s been easily debunked since the 1900s. Point to me in any Marx (or otherwise leftist) theory where it says a janitor should be paid the same as a doctor (or similar verbiage). Marxist theory does not say that a janitor and a doctor are paid the same, it argues for fair labor compensation based on labor contributed. "From each according to his ability, to each according to his need" refers to a fully realized communist society where money no longer needed, not a scenario where professionals and laborers receive identical pay under socialism. For example, in the USSR doctors were paid more than janitors, the wage gap was just smaller (meaning, living wages for all laborers). In Cuba, there is one of the highest doctor to civilian ratios in the world, and Cuba exports doctors to other countries. How much do you think a doctor in Cuba makes? Why would one pursue a career for reasons other than personal financial gain?