I don't think many experts criticize the idea of communism - just the fact that it is impossible to achieve in reality and historical or even anecdotal evidence supports this criticism.

I mean the history of human civilization between the advent of class society and the 18th century also had no evidence to support the "real life" viability of liberal capitalist rule.

Even then, for the first century of its existence, if you consider the number of failed revolutions that saw re-establishment of monarchial/theocratic rule, its failure to liberate slaves, engaging in the same imperialist tendencies as feudal states, violently squashing dissent, the constant market crashes, the corruption of the ruling class, the failures of political leaders to adhere to the constitutional law that they themselves wrote etc...an observer living under a prospering monarchy in the 1800s could also very well say

Ha! Meet the new boss - same as the old boss.

Well yeah it sounds good on paper but doesn't work in real life.

I'm not criticizing the idea of liberalism, it's just that history shows that it always fails.

Then, when the old feudal powers, for a time, were able to innovate their structures to accommodate industrialization, (domestic) slavery abolition, and demands for suffrage, they might also also comment

See? The system works - just very slowly. We don't need any revolutionary reconstitution of society that could jeopardize the current stability that is working in my favor

These traps of thought termination can be avoided by studying the dialectical materialist analytical method developed by Marx and Engels (and continually expanded by later generations), derived from examining the interactions of socio-economic forces within Feudalism that birthed Capitalism, and applying that study to the historical development of liberal capitalist society to sus out the transformative tendencies that would come to dominate the next major epoch of human civilization, broadly conceptualized as Communism.

In short, Communism isn't simply a set of "wouldn't it be nice if..." ideas. It's an observation of the evolution of human relations. Sometimes specific branches die off like the Soviets and Parisian communards, but there isn't such a thing as a "perfect stage" that evolution stops for, and it certainly isn't Capitalism. That doesn't necessarily rule out some third alternative, but so far it has only materialized as fascism and techno-feudalism, and neither to a Marxist are changes at all because the productive relations remain strictly Capitalist.