Marx was big on getting people to the place where they don't feel like their work is pointless. But in order to get there, you have to get rid of the social stratification of the current system, where some people do their labor and give it to somebody else to sell. That seller not only gets to keep the majority of the profit, but it also keeps the work from being very fulfilling since you're disconnected from the end product of your effort.

So Marx didn't say it was impossible. He just said that getting from here to there was going to require changes -- changes that could easily be unpleasant.