The primary argument of the atheist is
A1: a belief without evidence is irrational
from which it is deduced that religious beliefs are irrational. However, it is well-known that many atheists ("strong" atheists) also believe that deities do not exist, which is of course in and of itself a belief. In order to justify this position and remain consistent, the atheist needs the following two arguments
A2: a belief with ample evidence is rational
A3: lack of evidence is evidence
Let us grant them these premises. By combining them, the atheist concludes that since there is a complete lack of evidence for the existence of god, this is ample evidence that god does not exist, hence the corresponding belief is rational.
But the problem I would like to ask about is ... couldn't the very step just undertaken be replicated for infinitely many other things?
Specifically, take any object which is currently outside the boundaries of the imagination of the atheist. Such an object, by its very design, has no known evidence. That should be obvious. After all, if such evidence were known to exist to the atheist, it would require that they were aware of what the object was to begin with, in order for them to be able to link the evidence to the object. But they cannot even imagine this object, hence it is an impossibility to link any evidence to it, hence no known evidence exists.
Hence, there is a complete lack of evidence (from the perspective of the atheist, at least) for any object outside the realm of the atheist's imagination. By replicating the step from above by applying A3 and then A2, it would seem that the atheist is forced to believe that anything outside of their imagination cannot possibly exist. That is, the atheist considers themselves to have 'omnipotent' imagination, in the sense that anything the atheist fails to imagine, cannot possibly exist at all.
Is there a flaw in my reasoning? If so, please point it out. If not, what are the implications of this for the rationality of the strong-atheist position (to me it seems very irrational to believe that the universe succumbs itself to our imagination).