I agree that there is a common perception that universalists emphasise God's love and forget that He's also holy and just. But I don't think that's true. It's just that they think that God can't be divided up into opposing parts such that some of His actions are loving e.g. in salvation and some are about justice and wrathful.
They rather see all of God’s actions as motivated by "holy love". Everything God does is holy, completely just, and completely loving.
So whatever being wrathful and hell is about it must be compatible not only with justice but also with love. Which means that it must, in some way, have the good of those in hell as part of its rationale, which is obviously not possible with ECT.(Eternal Conscious Torment).
Universalists feel that the error with ECT or annihilationism is that while they make much of God justice and wrath they are incompatible with His love and, as a result, they divide up the unity of His nature.