Not only do Marxists have theory, we also have practice. Practice doesn't look different from theory, actually, you'd know this if you actually understood that Marxists reject the perfect utopian wonderland from earlier socialists like Robert Owen. There is diversity in opinion, spirited debate, and many different perspectives. The bourgeoisie is indeed oppressed, as they should be. Socialist states do indeed have prisons. The "millions of deaths" you hint at, in reality, corresponds to far fewer deaths than the victims of liberalism and capitalism.
I have spoken with people that grew up in socialism, and current citizens of socialist countries like the PRC. I don't rely on anecdotes for my stances, I read historical texts, statistics, track metrics, and engage with theory and practice. I don't care who your family member is, I can find Flat Earthers or those who think the US is the greatest country on the planet. What matters is the actual, on the ground facts.
Industrialization in a planned fashion, with a direct focus on uplifiting the proletariat, was the cause of uplifting from poverty. Without Marxism, using England as an example, capitalism skyrocketed poverty. The working class had it far worse than as independent peasants for a long time, life expectancy dropped, and it was only when the proletariat began to organize violently did concessions come and begin to eventually surpass feudalism in England. In socialist countries, the impact was immediately positive.
You're deeply unserious.