The reason is simple. Lenin not only lucidly wrote about the contradictions in our own system, which go so deep that they cannot be resolved by minor alterations or incremental "progress", he also wrote about what to do. He wasn't a moralist or utopian trying to show his virtue.

What is dangerous about Lenin is that he talked about actually destroying the system in reality, not just theorizing about what is wrong with it. In other words, Lenin was serious. This kind of thing can't be tolerated. It can't even be discussed, apparently.

What would we say about the USSR if Adam Smith was never taught? Never discussed? Most Americans hate communism, but can't define it. What would we say if Soviet citizens hated capitalism without reading capitalist thinkers?

We'd call it brainwashing, censorship, and propaganda.

In America, the supposed land of free speech, we cannot even debate whether or not we should change our own economic system. Anyone who wishes to get rid of capitalism is banned from every institution with any power over our ideas. We do not have academic freedom, or free speech.

In conclusion, if you believe in free speech you owe it to yourself to read what every powerful institution doesn't want you to read. And it isn't conservative hacks who bemoan censorship while getting book deals and TV interviews.

It is Vladimir Lenin, the real threat to power.

Resources on Lenin:

What Is To Be Done?
https://www.marxists.org/archive/lenin/works/1901/witbd/index.htm

Imperialism, the Highest Stage of Capitalism:
https://www.marxists.org/archive/lenin/works/1916/imp-hsc/index.htm

State and Revolution:
https://www.marxists.org/archive/lenin/works/1917/staterev/index.htm