There can only be one way at one time. Decisiveness trumps by default. I do expect bluntness and sternness from many SX and SP doms more often than from SOs.
I don't quite understand what you're saying. What "one way" at a time are you referring to? The fact that I said being hard and fair? Of course you can be both of those at the same time (unless I am misunderstanding what you're referring to).
Depends on person. Some need it others dont. The person who is hard on themselves don't need it, the people who are not may or may not. Depends on how much they push themselves. It's possible for someone to push themselves hard without being hard on themselves. They do what they can and they are happy with it. Also, people are hard on themselves in certain ways and not others, so that comes into play as well.
This is an important point to clarify. Being hard on everyone all the time without discernment on when it should be used is paramount. Further, being hard on some people is completely unproductive. The only time to go against that is if they need to be punish or something like that, and even then that still needs to be judged carefully.
I'll use my research adviser, and another professors down the hall as points of comparison and contrast with respect to this. Both of them are quite hard on their students, though I'd argue my adviser is a little more hard than the other. It would depend on how you look at it though. Either way, my adviser expects a lot out of us. He's constantly pressing for us to be productive, get results, get to the next step, and make significant progress. If we're doing poorly, he will bluntly tell us, and tell us that we need to do better. Usually he'll be specific on what's wrong and how it should be improved.
The other research adviser down the hall is the same. He's also very hard on his students and expects a lot. However, each go about it differently. My adviser has the standard of "get the work done". He doesn't care how you do it, when you do it (within reason of course), and sometimes even how you do it. It's a simple question: "is work getting done? yes? great!". The other adviser, not so much. He has much more rigid rules. Benchmarks of hours one needs to be working, number of reactions that need to be done, logged and scheduled vacation time, and does not tolerate or care to understand when someone is upset in a way that is not immediately apparent to him. Where as, my adviser is understanding and will consider if and how someone is upset, and attempt to accomidate to it. He looks at the individual and determines exactly how to be hard on someone that is helpful to them. The other adviser has a universal measure applies the same to everyone.
Both are hard, but one is much more "appealing" to work for. Granted, some people prefer the other one, but it's often for other reasons outside of this. It comes down to understanding of the individual, and recognizing that being hard on someone is most effective when it's done in a broad big picture setting. That's not to say that he doesn't have universal standards, he does, he just sees where they can go wrong and will work around them for a given situation.
As for enjoying it - when it must be done, the person who will enjoy it is the wrong person to do it.
Why? Just because someone is being hard doesn't mean they're being sadistic about it. There can very well be very virtuous well founded reasons for enjoying being hard on someone. If they're spawned of ill-will or unjustified reasons, then yes it can be bad. Otherwise, I don't think so.