Against a horde of monsters, yeah.
I just can't see old Eren being so bent on revenge that he'd commit mass murder and indiscriminately kill civilians, becoming just as bad (even worse, really, considering he's not an ignorant kid) as the very people he swore revenge on.
The dumbest part about all this is that it's largely pointless or even detrimental.
First, the main victims of his slaughter were:>Potentially innocent people, including children. >The incompetent officers who the competent officers wanted dead>A bunch of ultimately expendable ambassadors
Second, he solidified Paradis's role as the bad guys. If there was ever a chance at rebutting Willy, pointing out Marley were the ones who started this shit by kicking the hornet's nest in the first place, and at least trying diplomacy with the other nations, it's gone now.
Third, he fell for the bait and ate the wrong guy. Then after sucker punching and flooring the real War Hammer Titan he STILL got his ass kicked and needed to be saved.
Fourth, even if he or the SL kills Magath and War Hammer, it doesn't mean shit because Marley is the most behind in conventional warfare and titans are outdated anyway.
Fifth, the SL blew their element of surprise on the mainland dragging his ass out of the fire. If they had decided diplomacy was futile, the window of opportunity for ambushing all the other important targets has already closed. Wanna compare Eldians to Germans? This is the part where Italy's foolishness causes the Spring invasion of the USSR to get delayed.
In conclusion, Eren is a total fucking retard whose strategic disaster would make Erwin want to strangle him.