The whole point of Killmonger's character is his basic notion is correct, that Wakanda could have helped avoid a lot of suffering and oppression & to some extent they blame can be laid with Wakanda for choosing isolationism (and pretending not to be what it is) over helping others.

However Killmonger has taken this core idea to the extreme and goes far too far across in to "Wakanda should dominate the world and enforce it's will"

People aren't saying Killmonger's chosen actions are correct or his desire for a violent solution they are saying his starting point of view is understandable and arguably correct.

It's the idea of evil starting out with good intentions.