The phrase you used crossnote "a belief already held by most before 325AD" is simply not true.
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Like many third-century Christian scholars, Arius was influenced by the writings of
Origen, widely regarded as the first great theologian of Christianity.[SUP]
[14][/SUP] However, while he drew support from Origen's theories on the
Logos, the two did not agree on everything. Arius clearly argued that the
Logos had a beginning and that the Son, therefore, was not eternal. By way of contrast,
Origen taught that the relation of the Son to the Father had no beginning, and that the Son was "eternally generated".[SUP]
[15][/SUP]
Arius objected to Origen's doctrine, complaining about it in his letter to the Nicomedian Eusebius, who had also studied under Lucian. Nevertheless, despite disagreeing with Origen on this point, Arius found solace in his writings, which used expressions that favored Arius's contention that the
Logos was of a different substance than the Father, and owed his existence to his Father's will. However, because Origen's theological speculations were often proffered to stimulate further inquiry rather than to put an end to any given dispute, both Arius and his opponents were able to invoke the authority of this revered (at the time) theologian during their debate.[SUP]
[16][/SUP]
[edit] Initial responses
At first, Bishop Alexander seemed unsure of what to do about Arius.
The question that Arius was raising had been left unsettled two generations previously; if in any sense it could be said to have been decided, it had been settled in favor of opponents of the homoousion (the idea that the Father, Son and Holy Ghost are of the same exact substance and are co-equally God; the position adopted by the Athanasians and Trinitarians who opposed Arius). Therefore, Alexander allowed the controversy to continue until he ultimately came to believe that it had become dangerous to the peace of the Church. Once he reached this conclusion, he called a local council of bishops and sought their advice. This council decided against Arius and Alexander
deposed Arius from his office, excommunicating him and his supporters. Later, Alexander would be criticized for his slow reaction to Arius and the perceived threat posed by his teach(Wikki)
It would seem bookreader you are correct