I believe the word you're looking for is nihilists.

Stuff I want to matter, matters.

Why wouldn't it. Sure matters to me as do others' lives.

Yeah, damnable, know it all atheists infiltrating an agnostic oasis. If atheists are wrong or right "why does anything matter at all" to you?

U R correct - it would Not matter -
as thine - Essence is Not matter -

yet without such - One cannot Know experientially -
that which is thy - Self being a Person - thru a human -

as such the Reason & Meaning of - Life as a human -
is to express & thus experience - Whom U so desire -
to Know thy Eternal & Divine - {Self Soul Spirit} - AS -
while U R being a Magnificent yet mortal - human Being -

Things “matter” to those who chose to derive meaning from them.

My main objection to religion is that it destroys the need for that very important question "Where is the evidence" . The underpinning and confidence generated when what does get confirmations with evidence means that everyone can follow that evidence and accept a belief. Without it we know that the gullible are not thinking and are likely to suffer harm to mental Health. I accept that some do survive in blissful ignorance of the damage that religion can do.

It only matters while you're here. After that it doesn't matter.

If I bite into a hot chilly pepper, it matters, and I spit it out. At that level most things matter, to some degree. It is however very arrogant to assume that the universe owes us an explanation of any higher meaning, whether one be there or not. Maybe we will never have an understanding of meaning, but also maybe there are more intelligent species out there in the universe, to whom the issue of meaning and why things matter, is a simple problem.

There could be great cosmic meaning without god, we don't know, the existence of meaning, and humans knowing that meaning are two different things.

If an atheist said, 2+2=4, they would be right. However, 2+2=4 has nothing to do with atheism. Correctly within the context of the definition of atheism, atheism is incorrect, or illogical.

That is an absurd question in and of itself. It is not religion that determines if something matters.

Is the presence of god required for the presence of meaning?

It doesn't really, our planet could vanish and not change anything significant in the cosmos. I've had nihilistic thoughts for years now and I've come to the conclusion, we don't matter. Everything as we know it is temporary, therefore almost meaningless. If you meant something else let me know, I enjoy this topic.

On a cosmic scale, nothing does matter at all. The universe doesn't care about whether we exist or not. But, because we have evolved to understand that we exist, and with the ability to feel emotions, to empathize, we are able to give meaning to things, to life.

I don't understand the idea that the only way life has any meaning, or that it matters, is because some being created us, or the universe intended for us to exist.