The fact that Arius was well spoken, and rather influential, meant that his words and ideas had a lot of weight. By contrast, one of the main voices contra arius at Nicea was a young and relatively unknown Bishop named Athanasius, who insisted that Christ was of the same substance with God the Creator. It was a really long argument, which to this day makes very little sense to anyone outside the church, but which resulted in the Nicene Creed, the one creed that unites almost all Christians, saying:
We believe in One Lord, Jesus Christ, the only Son of God,
eternally begotten of the Father, God from God, Light form Light,
True God from True God, begotten, not made,
of one Being with the Father...
Arius wasn't a bad guy, he was just theologically wrong, and declared so by the church as a whole, which is what being a heretic is all about. As an interesting post-script, Arius actually managed to become best buds with the Roman Emperor Constantine and ended up wielding a lot of influence in this new thing called the Holy Roman Empire, so you know, being a heretic can't be all bad.
On the other hand, being apostate is what I think most people really think about when they hear the word heretic. An apostate is one who has cast off, not just the doctrine of the church, but the mores and ethics as well. An apostate has lost or broken faith, they do not just disagree with some point of doctrine, they come to despise the whole system. The example that springs to mind are folks like Alastaire Crowley and Anton LaVey, who actually decide that they like the character of Satan better than the character of God. Strictly speaking, they are not heretics, they are apostate, because they don't proclaim a different faith, rather they are faithless. While most of these things proclaim some sort of allegiance to a biblical character (Satan, the accuser or the adversary), they actually consider God to be a mythology, so rather than rallying to the rather austere banner of atheism, they figure why give up on all the good religious fun, let's just take up with the enemy. It's really nothing more than secular humanism with pentagrams and capes. It certainly doesn't deserve to be considered heresy, that would be insulting to heretics.
That is, of course, an extreme example. Most forms of apostasy are much more subtle, and far more destructive to the life of the church. Apostasy is simply not caring, and deciding that it really doesn't matter. The church, through it's councils and doctrines, has learned to deal with heresy rather well. We haven't tortured or burned anyone at the stake for centuries, we just argue it out, in long drawn out ways that no one on the outside understands or cares about.
Apostasy on the other hand really seems to have our number, it pushes all the right buttons, and can really get us wound up. Even though it can be silly and cartoonish at times, it gets us on its' own turf so easily we barely know what happened, and pretty soon we're holding up signs and spouting slogans, and doing things that quite frankly probably make Jesus cry. Our arguments with heretics may not always be our finest hour, but our futile struggle with apostasy is just about our low ebb.
We can debate the finer points of doctrine with great eloquence and, in our best moments, inspired grace. What we can't do, especially in the modern world, is force a willful apostate to care that Jesus loves them.
That doesn't stop us from trying, and it certainly doesn't stop it from being true.