Arianismworse than other heresies, because of Persecution
The other heresies also, when the very Truth has refuted them on the clearest evidence, are wont to be silent, being simply confounded by their conviction. But this modern and accursed heresy, when it is overthrown by argument, when it is cast down and covered with shame by the very Truth, immediately endeavours to coerce by violence and stripes and imprisonment those whom it has been unable to persuade by argument, thereby acknowledging itself to be anything rather than godly.
For it is the part of true godliness not to compel, but to persuade, as I said before. Thus our Lord Himself, not as employing force, but as offering to their free choice, has said to all, 'If any man will follow after Me;' and to His disciples, 'Will you also go away?' This heresy, however, is altogether alien from godliness; and therefore how otherwise should it act, than contrary to our Saviour, seeing also that it has enlisted that enemy of Christ, Constantius, as it were Antichrist himself, to be its leader in impiety?
He for its sake has earnestly endeavoured to emulate Saul in savage cruelty. For when the priests gave victuals to David, Saul commanded, and they were all destroyed, in number three hundred and five; and this man, now that all avoid the heresy, and confess a sound faith in the Lord, annuls a Council of full three hundred Bishops, banishes the Bishops themselves, and hinders the people from the practice of piety, and from their prayers to God, preventing their public assemblies.
And as Saul overthrew Nob, the city of the priests, so this man, advancing even further in wickedness, has given up the Churches to the impious. And as he honoured Doeg the accuser before the true priests, and persecuted David, giving ear to the Ziphites; so this man prefers heretics to the godly, and still persecutes them that flee from him, giving ear to his own eunuchs, who falsely accuse the orthodox. He does not perceive that whatever he does or writes in behalf of the heresy of the Arians, involves an attack upon the Saviour.
Source: Historia Arianorum (New Advent)