I have to disagree about the 'clean' bit.
A pass almost certainly needs some sort of cover to justify the move.
Although it IS worth learning some other 'break/control' methods, such as a double undercut or a side slip. Varying your controls is paramount to stopping the effect looking too mechanical.
In my opinion, the pass is not the be-all and end-all. In fact, I believe it to be possibly the most overrated of sleights.
It's great when it first 'clicks' into place. But then it becomes far to relied upon.
Also, I disagree about a side-slip being less efficient?!?!?
A side-slip is very pure, especially if the card is stolen into a lateral palm for example. The pass involves bringing the card to the top THEN moving it on, whereas the side-slip is a continuous move for stealing a card.
Perhaps I read a different book

I think Mark hit more of a nail on the head with the guilt thing.
A pass is by no means invisible. But it can be hidden well, if your technique is strong.
Learning the pass requires patience, and a lot of time spent in front of mirrors.
