Capitalist vs The Laborer

In class we discussed "capitalist vs the laborer". Marx view point about how the poor and the laborer will make one big middle class got me thinking. How is that even possible? Even if people are covered for like in a socialist country, there will still be poor people. The system will not work for everyone's situation or it will work to some extent. However, I feel as though it would not be possible to have one big middle class.