Someone else will pay for it... the evil rich. Never underestimate the mobocracy lead by demagogues or the havoc they will cause.
But that is the problem they have. If they "tax the rich" enough to fully pay for their pet programs, the few rich that don't move their wealth to other countries will go broke. You could tax the "evil rich" at 100% and still not be able to pay for all of the leftist programs we have right now. The only way they are supported right now is by massive borrowing and by taking the true cost of Social Security and Medicare off the budget.