There's something clearly wrong with saying you adhere to an "ism" based only on you not being convinced of the arguments for another "ism".
"Isms" have NEVER been about merely "lacking belief" or "just not being convinced".
"Isms" are ALWAYS about positive affirmations of some kind. Thus, there is a burden of proof for BOTH SIDES when two opposing "isms" clash.
What's more ironic is that they'd require "evidence" to believe theism, but they believe atheism on the basis of lack of evidence. That's a freaking logical conundrum.
if you ask them "are YECers justified to believe YEC, due to not being convinced by evidence for evolution?" They'd say no.
If you ask them "is one justified to believe supernatural creation of life on Earth, due to not being convinced by evidence for natural creation of life on Earth?" They'd say no.
However, they believe their atheism, because theism fails to convince them. Go figure.