There are interest conflicts between the workers aristocracy and the other workers. There are interest conflicts between the workers in job und unemployed ones. There are interest conflicts between unionized workers and the others. Another barrier for the unity of workers is, the growing income differentials between workers. Marxian theorists try to refuse the implications of these differences.
Today there are big income differences between workers.
There is substantial workers aristocracy in rich countries. Another strange view is about 'needs'. Marxian theorists claims that under capitalism , production is for profits, not for human needs. May be it is more correct to say that the production is for capital accumulation under capitalism. But if you stop here, this statements becomes an obstacle to see the other side of the coin.