This is very interesting discussion. I too scratched my head a little bit at Sean's viewpoint that Mal is a bully. Although I haven't rewatched Firefly recently, I've seen every episode enough to know it fairly well. But, like Solai did, I'm lookng forward to taking another look with the "bully" question specifically in mind.
Here's my take: Malcom Reynolds is, I think, keenly aware of what's required to be an effiective captain of a ship. And moreover, Mal is essentially the captain of an independent small business. Whether he and his crew eats, survives, profits and keeps flying litterally depends on his decisions.
On top of all that, Mal has been burned by the fact that his decisions (and other's) during the war ---of choosing to stick and fight, has cost lives. So he's wary of getting burned that way again.
I don't know of any case in the show where his seemingly "bully"-like actions weren't motivated by the desire to keep Firefly and her people safe and flying. Being a leader means you have to 'kick people's ass' sometimes even when you don't feel like it.
Also, as Joss Whedon remarked on one of the commentary tracks "Mal is an uncomprimising guy."
All that said, Nathan Fillion, sure does know how to play a convincing bully

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