A lot of 20th century Latin American literature has knife fights and similar displays of male bravado as a recurring theme. Some of it has permeated to tango lyrics - Mandria and La Cicatriz come to mind. I'm not an expert in human behavior, biologically or sociologically, but some of the observations I've made in milongas make me believe these instances of male to male aggression are more than simple displays of their manliness. Without going too deep into history or geopolitics (admittedly because I don't know enough about it to go into too much detail), most human conflict can be traced back in some way to competition over resources perceived to be scarce, or actually scarce. In the milonga context from the male point of view by far the two 'sources' most competed for are space and women. Men fighting over women (and vice versa) seems to be universal, encompassing all cultures and historical times... from the Trojan War in Greek mythology to basically every other cheesy Latin American telenovelas.
The attitude over space seems to be more specific to each community and each culture. It is said in Buenos Aires that different styles of dance were born depending on the availability of space, with downtown tango giving birth to tango milonguero, and suburban tango giving birth to tango salon. And maybe this is why tango nuevo is so dominant in the US, in general terms being one of the most sparsely populated nations in the developed world (but it doesn't explain why oh why tango escenario is so popular in Japan and London... there's probably a myriad of other factors I'm overlooking). Indeed, back when I lived in small town America, the milongas were so huge and the attendance so small that you essentially had a whole stage for yourself to experiment. The line of dance was merely a fictitious concept talked about in class, only existent in parallel dimensions where milonga real estate was a big issue. The idea of a couple dancing less than 1 meter in front of you and another less than 1 meter behind you was an alien one, almost inconceivable.
Argentina is one of the two biggest powerhouses of Latin America and has been known to periodically exercise their power over their neighbors. In addition, culturally Argentines are notorious for their arrogance, their ingrained belief that they are somehow superior to the rest of South America because they have a higher proportion of European blood in them. My theory is that these two elements combine together to give Argentine milongueros a profound sense of territoriality, and it gives them not the right but the obligation to react in a potentially aggressive way to any trespassing of their personal space. In fact, a visiting Argentine teaching couple said that disrespecting another man's personal space in the milonga by not following the line of dance or otherwise was about the gravest insult you could give to his honor.
On the other hand, the undisclosed nation I reside in at the moment, while doing better than Argentina economically, historically is a weakling in the region and has been subject to constant bullying from neighboring powerhouses all through its history (I think one of these days a smart ass blog reader will collect enough hints about this 'undisclosed' country and community to not only figure out what country I'm talking about, but who I am and who all the people I'm talking about are... and I'll be in some shit). Given such historical precedents, I suspect people here might be displeased by invasions of their territory, but in a way used to it, and as such may be reluctant to do anything about it. This past weekend, however, there was an exception where a fight almost broke out because of a clash between two couples. I don't know the exact details because I only heard one side of the story, but I later saw the two men walk outside the milonga, and I was expecting an old school knife fight to happen, or if not a fist fight at the very least... It turns out they talked it over. Lame. But anyway, nearly everyone saw the incident. Maybe because of that, leaders were more careful that day in LOD and space issues. It was one of the best milongas I've been to in that sense. People should be wary of territoriality at all times in a milonga without the need of such an incident to break out.