When does a tax deduction become a tax loophole?

The word “deduction” sounds virtuous and legitimate. The word “loophole” sounds dishonest and sinful. The President approves of certain deductions. He seems to hate loopholes.
If I take a deduction on the interest on my mortgage, is that a virtuous declaration, or am I exploiting an immoral loophole.
Assuming all legal deductions are legal, why are some of them regarded as laudable deductions, and others regarded as shitty loopholes.
Is it the deduction, or the people who claim them that is problem?
And who gets to judge which is morally justified and which is immoral and worthy of disdain?