Really? You think "theological differences of opinion on the character of historical figures" is insignificant yet "spitting hate at groups of people" in response to their "spitting hate" at those historical figures is worse?
Yes because the latter leads to hatred and excusing violence
in the world right now while the former will at worst damn people in their own afterlives, which is bad sure, but it's their own business.
If someone makes it part and parcel of his belief to hate and insult those who you revere as those who are some of the closest to Allah, then what does it speak of your love that you refuse to even speak out against those who do so?
How did the Prophet Muhammad respond to the insults, taunts, and jeers of the people of Mekkah before the Hijra?
We are a species that is not perfect. We have to judge to create a functioning society as law and order are necessary. But we have to remember that we make mistakes and only God is perfect. Once we lose sight of that we start getting arrogant and take upon ourselves tasks that are reserved for God. One of these is deciding who is a true Muslim or is not. That's not something we are qualified to judge. But you are doing so. So are the Nasibi spouting idiots. Do you really want to act like they do with the Rafidah nonsense?
Similarly, if someone insults the companions and the wives of the Prophet PBUH constantly and makes it part of his creed, is it not considered a great injustice?
They harm only themselves in their afterlife if God's judgement is punishment. Injustice visited on the living is something we can do something about by refraining from divisive partisan and insulting slurs right now. God will take care of any slander towards the dead.
48:14 and 3:129
And to Allah belongs whatever is in the heavens and whatever is on the earth.
He forgives whom He wills and punishes whom He wills. And Allah is Forgiving and Merciful.
Do you know what God's will be in the day of judgement? Do you know who will be punished and who will be forgiven? No you don't. So why act like you do here and now? Why persist in defending language that causes rancour and is used to justify evil acts? You can disagree with Twelvers all you want and enagage in debates but you are taking it too far.
2:190
And fight in the way of Allah with those who fight with you,
and do not exceed the limits, surely Allah does not love those who exceed the limits.
What are the limits? Only God knows for certain but the verse shows clearly that limits are there. We should be cautious and humble when we try to fight for God with our words. Using insults and demeaning slurs has to be, at best, close to the line because it adds nothing to the debate but instead poisons it and makes any attempt at dialogue toxic, breeds hatred, and encourages extremists to attack innocents like happened last Friday.