Paul has indeed defended earmarks, and has even advocated expansion of them. I'm not quite sure of his rationale for it.
But at least in today's environment, it's irresponsible. One analogy that I read long ago was that being elected to Congress was like being given an American Express Card.
You could spend as much or as little as you wanted, but you only had to pay 1/435th of the bill.
If you spent extravagantly, you only paid 1/435th of the bill. If you spent nothing at all, you still paid 1/435th of the bill.
It's a big simplification, but it's a good way to demonstrate how it doesn't encourage fiscal responsibility.
“Paul has indeed defended earmarks, and has even advocated expansion of them. I’m not quite sure of his rationale for it.”
Because the Constitution give Congress, not the Executive, the power to spend money
His rational is that if the money is earmarked the money goes where it was intended to go. If not the money goes into a general "slush fund" that the administration can spend anyway it wants.