In the first thread I think the guy may have been justified in his use of the stick as a weapon. There were multiple opponents and therefore a disparity of force. He had also attempted to flee first rather than escalating. I'd say that the only way that he wouldn't be justified is if there had been an exit that he could have easily fled through in the back of the McDonald's and he chose to instead stand his ground and fight.
Now, whether he was justified in continuing to strike his attackers once they were down on the ground is another story. Unfortunately, we can't tell from the video what the two women attackers were doing while on the ground because the counter is in the way. As I understand use of force laws (and they can vary from state to state/country to country) you are justified in using sufficient force to stop the attacker. Once they are neutralized though, you don't have the right to continue assaulting them (and that's pretty much what you're going to get charged with at that point).
I think he may have gotten himself into trouble by not realizing this distinction.
In the second thread, I think that the guy was foolish to involve himself in a fight that he had no stake in. I can understand wanting to diffuse a violent situation before anyone gets seriously hurt, but he doesn't have the legal right to use physical force in that scenario. His best bet would have been to call 911 and then only choose physical force if it looked like there was immediate risk of serious harm to one of the individuals.
Now, had it been a perceived mugging, rape, murder or other violent crime, or had one individual been at a considerable disadvantage (like one was a 120 lb woman or child and the other was a very large man, one had a weapon, etc...) then maybe I could see trying to "protect/defend an innocent" and he could have probably pled the good Samaritan defense. Also, in such a situation (especially had the perp had a weapon) I would actually agree with not making one's presence known prior to launching into physical force. You want the element of surprise in that case.
He also made no attempt to diffuse the situation by verbal means or get a more clear idea/picture of what was really happening with speech prior to using force. That was a mistake on his part. Had he just said, "Hey! What's going on here?! I'm going to call the police if you two don't stop it!" The two people would have likely stopped dancing and told him that no, everything was fine. Had he been afraid that speaking could have put him in danger, he could have first found cover (hidden behind the corner of a building for instance) and been ready to run for it should one of the individuals have tried to pursue him.
Either way, given the situation (or at least the description of it we have), I think he made an erroneous decision and subsequent actions.