Old but gold.
Violence is not to be used lightly but it is necessary sometimes. Love for something assumes hate for everything that seeks the destruction of the beloved.
Regarding sinners we have to remember that: (1) we are them, so we have to be very carefull on what we recommend for sinners; (2) From salvation point of view all sins are soul destroying, but from social order point of view some sins are worse than others and may require violent cohercion; (3) Violent cohercion does not mean we do not forgive the sinner or that we hate him, but that we are preventing his mistakes from impacting the innocent.
Arius was guiding thousands of souls to hell, possibly gaining money from the name of God. And for that he got a punch on the face only. The evil he caused is immensilly disproportionate to the reaction of St. Nicholas, which, in comparison, was mild and contained.
Much as I hate to rush to the defence of Arius, it seems to me wrong to speculate about simony on his part. A great deal of anti-hagiography was written about this and every other heretic, but you have to recognize where the truth likely stops and demonization begins. And it surely has begun when we are hurling accusations not to my knowledge made by St. Athanasius for example.
Which is also what this thread comes down to. Arius became convinced of a lie and Eusebius of Nicomedia identified it as a means to facilitate his personal climb up the greasy pole of late Roman politics. St. Athanasius was about the truth. Eusebius of Caesarea managed to avoid being declared a saint because of his desire to compromise with falsehood.
It seems to me therefore entirely appropriate that we yield to the most well attested interpretation of these events, in which St. Nicholas erred but due to his personal holiness there was a degree or perception of divine intervention that caused the Council to reinstate him.
If I were to read this cynically I would propose the fortunes of St. Nicholas shifted when the majority of the council began to accept the arguments so boldly presented by St. Athanasius and could see Arius was a sinking ship. It seems not beyond the realm of possibilities that there was a dark, grubby side to this council, but it was not to be found in either the persons of Ss. Athanasius or Nicolas, who were holy and God protected, even when in the case of the latter he sinned by losing his temper and striking Arius, although I'm sure Arius had it coming. There are many heretics alive today that I would enjoy slugging were it not for the moral restraint the Church provides.
And this moral restraint requires us to affirm that striking another in the manner of St. Nicolas is sinful.
However, I have the highest regard for St. Nicolas. His mercy and generosity shine through after sixteen centuries. Forensic analysis upon what are thought to be his relics makes my heart bleed for him, for his nose was broken at least three times; we know he was horribly tortured in the Diocletian persecution and can attribute this to that.
I think St. Nicolas however is better remembered as the benefactor of children and a confessor of the faith than as a heretic-beater.