I’m glad you’ve asked this question, since I was confused by the closing of the earlier thread.
The answer, of course, is “no”. An anathema only exists (in this context) as a consequence of heresy (which, the Catechism tells us, is “the obstinate post-baptismal denial of some truth which must be believed with divine and catholic faith”).
What are these truths? They were formally defined by the First Vatican Council:
by divine and catholic faith all those things are to be believed
[list]*]which are contained in the word of God as found in scripture and tradition,
*]and which are proposed by the church as matters to be believed as divinely revealed,
*]whether by her solemn judgment
*]or in her ordinary and universal magisterium[/list]
So, if Nicaea anathematized those who held to Arianism, it only affected those Christians who continued to hold to Arianism subsequent to learning that Arianism was a heretical belief.
Therefore, the answer is “no”. Those who held to Arianism prior to the council were not anathematized… unless they continued to hold to the belief once they knew that it was not an authentic teaching of the Church. It would have been their belief subsequent to the formal declaration, and not their belief prior, that would have brought with it the ecclesiastical penalty.
Let’s take the argument one step further, since that’s where we tend to encounter the ‘anathemae’ these days:
Trent anathemized those members of the Church who professed belief in a number of notions (that is, those notions introduced by ‘Reformation’ theologians). Does that mean that all who believe in these notions today (i.e., current-day Protestants) are held as ‘anathema’ by the Church?
The answer here, too, is “no.” The Church only pronounces ecclesiastical penalties (these days, the analogous penalty is known as ‘excommunication’) upon those who are members of the Church. So, the Catholic Church does not excommunicate those who are not Catholics. (In other words, if you were born into a Lutheran family, or were baptized into the Lutheran Church (having never been a Catholic previously), the Catholic Church does not declare you to be ‘excommunicated’.)
Does that help?