“Muh Human Nature” is a classic debunked liberal argument against socialism/communism. If you think you are ‘left’ then you really should maybe read some theory or watch some youtube videos or something. Second Thought has a lot of good intro to political economy explainer videos.
The larger point is that the workers that lack solidarity (as you claim), are specifically incentivized to think in this way by their boss under capitalism. “Crabs in a bucket” mentality is a good shorthand description of what I am talking about. The capitalists and bosses want workers to be in competition with each other, not in solidarity (think union organizing). This is why I called out your ‘class traitor’ thinking espoused by your comment. Brain worms refers to this. You have bad ideology in your brain due to living in the world of neoliberal capitalism, it has instructed you on how to understand the world. And you seem just fine with following those instructions to the letter.