Atheist is really an nonsense term as it covers such a wide gamut of individuals, from those who attack religious belief to those who simply have no religious belief or no knowledge of God(s) such as toddlers.
Atheist means disbelief in God or technically "Without God".
Yet we have no noun for somebody who disbelieves in Ghosts, Unicorns, Aliens, Yetis nor Leprechauns.
So why have such a stupid term to cover non-believers in God??
Basically it is a way of grouping together non-conformers to a religious belief so they can be derided and ridiculed by the religious Usurpers.
There is no term for people who don't play Chess.
So if Chess players decided to drum up public hatred for non-Chess players, then how would they do that?
Yes, they would create a derogatory term to cover all those who don't play Chess.
Just as Islam has coined the derogatory term of Infidel to cover all non-believers in Allah.
The same is the reason for the term Atheist.
So Atheist is just a derogatory term to group the many different forms of disbelief and non-belief, including no knowledge of God, under a single term for the purpose of attacking and deriding them.
But what many Theists don't get is that the term has no Bite.
Most Atheists don't care and wear the term proudly!
Though it really is a Nonsensical Term.
It really means Nothing!
Let me start by saying that you spelled atheism wrong. (note that I did not capitalize it) this is because it is a broad term like theist.
Sure there is no term for people that do not believe in aliens but there is no term for those that do either, at least not that I know of.
Personally, I don't mind the term atheist and, as you have pointed out, I don't think other atheists mind either. Some are even so proud of it they are trying to implement a symbol that represent them like the religions do. These symbols all tend to look like a variation of the letter "A". Are religious people insulted when they are called "theists"? To the best of my knowledge, religious people don't use the word "atheist" to insult us but just to define the position. Sure, they could say "people that do not believe in god" but "atheist" has a better ring to it.