Mildly Infuriating

Okay - I shall do so.

You are wrong.

If you're going to base your disdain for the entire concept on a single work by a single author, then it would help if you actually read the work itself, rather than deciding what it says based on, I can only assume, something someone you know said offhand that one time.

So as a starting point, here's the whole work. Why not do a quick search through for the word "violence" and see if he ever advocates for it (spoiler: he does not). https://warwick.ac.uk/fac/arts/english/currentstudents/postgraduate/masters/modules/theoryfromthemargins/manifest.pdf

However, in his conclusion, he does say this of communists:

They openly declare that their ends can be attained only by the forcible overthrow of all existing social conditions

This is an interesting passage to interpret - the use of the word force in this passage is fairly vague, for example, overthrowing the status quo via legislation enforced by police would be considered "by force", regardless of whether the police use violence. This is because it is done not by allowing what Marx calls the bourgeoisie to decide to switch to communism, but by enforcing it through law.

Now, there's more to unpack here, so I'll break it into a couple of sections...

Revolution

Marx does use the word "revolution" a lot in his manifesto, however typically not in the meaning you're envisioning (ie an overthrowing of government) but instead the meaning a fundamental shift in distribution of power and wealth within a society.

Is violence ever acceptable?

As a thought experiment, imagine a country ruled by a purely evil autocrat. This theoretical autocrat abuses their power, harms innocent people on a whim and takes whatever they please from their citizens. There is no allowance for dissent, no democracy for the people to represent their interests.

Would it be acceptable for the people of this nation to use violence to remove this dictator from power? I think most people would probably say yes in this context.

So we have determined that in some scenarios, violence may be acceptable when it is the only possible way to overturn an oppressive system of government.

That's not to say that it's the only way any system can be changed, or that violence is acceptable when it can be avoided.

The consequences of violent revolution

While violent revolution will change the distribution of power, it also provides an chance for opportunists to abuse this power vacuum to consolidate it around themselves, under the guise of being part of that movement.

Good examples of this are, of course, Stalin in the USSR, and, as a non-communist example, Putin consolidating power in Russia during the USSR's collapse and its transition to oligarchic capitalism.

The geopolitics of 1840s Europe

Europe in the 1840s was not like it is today, especially in a political sense. The continent was made up almost entirely of absolutist monarchies, with no democratic systems to allow the voices of the citizens to be heard.

There was a wave of failed revolutions against the feudal systems under these monarchies across the continent, which, with few exceptions, were brutally crushed by the states with almost no change.

Understanding these circumstances, it is easier to understand why the idea of transitioning to an equal distribution of both political, and in communism's case, economic power through peaceful means would be considered not just difficult, but laughably impossible.

Many of the seeds of the modern democracies we enjoy today were planted during this period of turmoil, in part in response to Marx's manifesto.

Communism and revolution under modern democracy

Now we have the privilege of living under modern democracies across much of the world, we have an unprecedented opportunity to actually consider Marx's ideas for a different societal structure, and implement changes that would be for the benefit for all citizens through democratic systems.

But we need to actually have reasonable discussions about these ideas and their impact, and "communism=genocide" is not only wrong, but takes a hostile stance against the concept before even understanding what the ideas are.

Edit: wrong link