Can't Be Friends With Direct Reports...

We knew this, right?
I mean, I'm not naive. I know that there's that "line" between getting along with the people you work with and  being friends with those people - especially when you are their boss.
The day will come when you will have to discipline them or terminate them or there will be a disagreement and the friendship will suffer, yada yada yada.
Or, the backstabbing scenario, in which something you said or did is used against you later, yada yada yada...
So why is it so easy to fall into the trap of trying to be friends with the people you work with?
Perhaps its because you find no common ground with my peers - other people who have similar/equal positions to my own. Perhaps it's because you have no desire to be friends with your boss.
However you justify it, the bottom line is that you spend the majority of your day with people you can't be true friends with.  It makes you feel fake, and lonesome, too.
My boss recently called me an employee advocate.  This, coming from the guy who believes firmly in the "coach them up or coach them out" strategy of employee retention.
So what if I defend employees who make my work-life easier?  So what if I defend employees who may not hit all their metrics, but are reliable, available, and decent human beings?
But then, I feel like a fool when I discover that perhaps those employees aren't as loyal to me as I am to them.
I can't blame them.  They look out for themselves, as well they should.  I'm just as quick to "throw my boss under the bus" probably, when it boils down to a debate.
But what is meant by his comment of "employee advocate?" Is he implying that my loyalty to my employees is misguided, that there is something going on I don't know about?
En Garde!