Milky Way Natives Fighting Each Other in Androma

Side-note alien race doesn't seem to matter.

Unlike ME2, you have Krogans and Turians working under a human gang leader. Before this no one but Shepard could pull that off.

You'd think that for a trip like this they would check out everyone who was coming along to avoid stuff like this. But AI has been stupid about other stuff, so I guess this shouldn't be so surprising.

It makes you wonder all these people going nuts and killing each other... No background checks were done on these people? Story wise something monumental has to happen for all these people to go rogue... So I'm kinda reserving judgement for now

Head of Nexus security is a violent thug who got kicked off-station, there was some Nexus uprising, good number of AI folks are anarchists shooting at everyone and stealing is described as one of the main ways for a pathfinder to get new gear.
Hey, how about that next Andromeda Initiative recruitment vid? We gonna be a brave explorers!

I was thinking there might be some stowaways that caused trouble but then I thought 'No that is stupid they'd be there for 600 years god dammit David get your head in the game'

This, I think, is the answer.  They are angry at what actually awaited them in Andromeda and decided to go their own way.

It's like they didn't do any background checks whatsoever on the people they put on the Arks.

Shit goes down and everyone decides to look out for themselves. I was hoping there would be infighting among the ARK's and it seems like there will.

Either that or people liked too much what they found on Andromeda that they want to become their own thing an become hostile to the rest of the AI.

This probably will be the case.

Beef between different MWG species is a done theme.  ME3 handled it.

I think they'll be moving beyond that in MWG.

That one gang leader in the trailer has Krogan AND Turian working for her.

Which makes me wonder who had thought that having krogans aboard on the mission is a good idea, to begin with. But following the human chick lead is also a problem. I understand how Aria T'Loak could handle Omega, but bowing to a random human female is different, you know..

Maybe it was more like a prison boat where they sent their less agreeable people.... Like when the British sent their worst prisoners to Australia to get rid of them rather than killign them.

That's not relevant to what we saw in the trailer though. 
Also, I disagree. The salarians are responsible for what happened in the Krogan Rebellions. Have they didn't uplift the krogans, the war wouldn't have happened.
Every species has its negative side. 
The reason for having the krogans in Andromeda is the same reason as why the turians demanded their help from Shepard in exchange of their fleets. Because they're arguably, as a group, the most resilient and strong(organic) soldiers in the MW. They figured they might be needed in Andromeda.
Beside, it's not like they recruited a massive number of them in the Initiative. The bulk is formed by the four Council dominant species. Their numbers are probably fairly low, and along with the genophage, they're not that big of a threat.