Both capitalism and socialism are great in theory but impossible to put into practice in their pure forms. Each has to be combined with some amount of the other in order to work, at least at this point in human evolution.

And even with socialism, there is an encouragement for people to exploit others for personal gain. The only difference is that in a socialist system, the ones who are doing it work for the government rather than corporations. When a government official won't perform the service they are employed to do without a bribe from the one receiving the service (and this is common in socialist regimes), that person is exploiting others for personal gain. And in the more totalitarian socialist/communist regimes, the workers are exploited for personal gain by the central government when the product of their labor goes to enrich those in government at the expense of the workers.

Some people are going to try to exploit other people no matter what system is in place.

I should note that when I use the term socialist regime, I am not talking about countries like those in Scandinavia which are, in my opinion, a healthy mix of capitalism and socialism.