oh right when he was charging up the tattoo. yeah its been so long since i read that. goddamn the future girl had ass like no tomorrow.

You could be like those "misinformed" so allow me to widen your thoughts to not think so narrowly. Actions have consequences.
Rember this is a world with advanced technology AND magic, so their education is up to par

assassination seems like it'd work until the empire turns against you because you illegally killed another noble. This also leads to petty tricks like family abduction from the remnants of their families. Remember they are nobles; without getting rid of their status and wealth, they will continue to plot against you. In fact they were already planning on suppressing him just because he spoke against them in younger years.

Let's say a noble is accused of a crime. First, assassins sent to stop your outburst. Next, proclaim victims were beat for "disrespecting a noble". Now they have the right to claim the life of your friend legally and your enemy gets ahead playing politics while strengthening their position. Sullying the pride of a nobleman, they now declare war on you. All the people that you wanted to protect are involved anyway. You've now lost more friends to assassin plots, money to deal with them, gave the enemy time for espionage, to gather assets and allies, as well as spend their own money to raise an army against you.

Now, let's say through constant back and forth they get "punished" for their actions. Because they are a noble who will inherit the head position, the different factions will heavily reduce their crime if not throw it out altogether. This would become a favor to collect later. We already saw the attempt for punishing someone outside the faction on trumped up charges with the 2nd prince and margrave. Now you have an enemy who owes a favor to a powerful backer and backer ALWAYS help to make sure they don't lose their investment.

Unless the viscount took his own citizens hostage they could leave, but then that's not MC killing them that's the nobles making them suicidal pawns. Knights and assassins are usually the dirty hands of nobles, meaning they are just as guilty as well and knew their masters were trash. At the very least they would have known through rumors making their way through the ranks. The other nobles were in on it together. Those who were forced under still had the opportunity to reject the call to arms or turn on the higher ranked nobles while communicating with MC. Meaning this would have been their best chance to become a free noble. If they lacked decisiveness, it means they thought that MC wouldn't win. It means they didn't lack information; they just helped the corrupt nobles stay corrupt. Its impossible not to know what your superiors are like.

To shorten response, even if they had no choice (not agreeing though), there are many cases of revolution. The moment the army came to the doorstep they had a choice to overthrow the power.
2nd in war, anyone who holds weapons are not innocent. The goal is to kill each other.
3rd if they would have allowed the kid to just face punishment instead of hiding, the massacre wouldn't have happened. It's not mc dragging in others, it's the lord sending others out to execution.