This is not a topic I have much RL knowledge of but one question I can answer is the arsehole one... I do not beleive it is essential for a Dom to always be an arsehole in life. I think this perception is based on an alpha male stereotype of what a 'dominant male' acts like and is largely false - loud, rude (well, blunt anyway) and physically powerful. In other words, an arse. Now, I do not see anything wrong with those traits in moderation but it is when they are to extremes that they become a problem socially. It turns from 'dominance' to 'bullying' and there is a fine line between the two which is very easy to cross.

Now, I do not think that this stereotype is the only one a Dom can follow. You can be dominant and quiet - simply taking control of a situation without necessarily shouting about it just by appearing to be someone who knows what they are doing and able to handle any situation. Teachers do it all the time and it is largely considered that if you have to shout to control a class you have lost control. The best teachers can control a class through silence, merely their presence in the room is enough to instill a reaction.