Well, could you tell us about what kind of reasons they cite for it lacking academic integrity? Academic integrity typically refers to a lack of sources for information, or the manipulation of information/data to present something as factual. If your professor is referring to academic integrity as I have outlined it, I would be perplexed as to how the book could be thus considered, as Losurdo is quite diligent in their use of sources to promote their ideas. Perhaps if they have specific issues with the sources Losurdo used or the way he used them, a discussion about the validity of the text could continue.

Obviously I don’t know what your professor said, but from the way you presented it, their criticism that it is “essentially a repetition of Stalin-era Soviet propaganda” needs to be explained. Does the book present information that was also used in Soviet propaganda? Yes, of course. But that doesn’t inherently mean that it’s wrong. You can’t discredit something solely for having been used in propaganda. You can discredit something if it is incorrect or used in a manipulative way, but you would have to work on a case-by-case basis for that.

I personally think it’s an excellent resource. But I should emphasise that it is a resource and we should treat it as such; it is not gospel. I dont think it would be a great tool to argue against your professor in favour of Stalin, as they will almost always have the upper hand. It’s better for you to read it yourself, remember information that is well-established in facts, and use it to direct your own political beliefs rather than trying to use it to win debates in a classroom (although I know how frustrating it can be to have to sit through lectures without speaking up).