The moral case for socialism and marxism is pretty easy to make: we should have all an equitable share in the public good, we should have the only say in our workplaces, the rich should not be the only people allowed to rule over us in politics, etc. We have the moral right and duty for revolutionary change.

But the empirical case for socialism is also strong, what Marx had to say in Kapital is true. This graph is measuring the world rate of profit over time, as Marx predicated there is a general trend for the rate of profit to fall. If we want a strong economy and fulfilling jobs that can give us all wealth while healing the planet, capitalism cannot serve that and capitalism will always undo itself. We also have the historical right and duty for revolutionary change.

If you want to read more this guy does a lot of excellent analysis.