First off I won't push the topic because I know what it's like to have a prick on your tail because of conflicting ideas/mindsets. However you bring up a point which is directly involved with the reason why STG was studying the Yahg. Or at least the classified reason.
Axis (the Yahg) was being studied for a hormonal balance microchip, placed on the brain stem. It is close to what could be considered a "mind control" chip, however instead of controlling the person of interest, it controls their hormonal balance. The Salarians severely cut back on the amount of adrenaline and testosterone running through his system and made him a passive threat in the most. Though he had the capability to attack, he no longer had the basic drive that made him want to attack. It was a project they created in case the Krogan got out of control again, or if another thread (like the Yahg) popped up. Axis was their official guniea pig for the experiment.
The official story of course, (or what could even be considered official, no one but top clearance officers knew about Axis) was that Axis was being used to learn more about the Yahg, but like I said this was far from the truth. Axis did end up escaping from the project however, and even though he destroyed the panel used to supress the hormones, the chip still remains. If you've ever played DA:O, he'd be somewhat like Shale was, previously controlled, now free, but not taking his freedom for granted. He doesn't want to be an aggressive meance because his personality has altered for good, making him scared of what his true capabilities are. He'd probably get a medic or engineer to rebuild the panel, to surpress his rage.
Again, I do have other ideas, but I've had this character for about two years and have only played with him twice, (and once the roleplay barely took off.) It would be awesome if I could play him here. And do have wiggle room for more ideas used to simulate his hormones if you guys can think of anything. It would be an interesting plot twist if maybe one of Nova's enemies got ahold of the panel, and used Axis against his will to attack his team.