This argument can't be taken as honest or sincere, because with absolute surety I can guarantee that horrific injustices took place today that you have absolutely no concern about at all.
When somebody presents this argument, they are not honestly advocating for justice. What they are actually saying is that "by not adopting _my_ political views, you are acting out evil". Part of any person's political world view is how they choose the issues that they consider to be important, knowing that they only have the span of their short life, and the means of their limited resources to address the problems in the world. You have no right to demand that somebody make the same decisions in this respect as you do. It is absurd, it is hostile to the notion of free democracy, and it is a standard that no living person could ever meet.
And all of that is before you account for the fact describing something as an injustice in the first place is quintessentially an opinion. This sort of thing reminds me a lot of the psychology of warfare, where soldiers are systemically taught to view the enemy as animals who lack humanity. It has a terribly toxic influence on society. Your ideas no longer need to compete on their merits, because the people who disagree with them are the enemy, and the enemy is less than human.