Humans hold beliefs about all sorts of things based on little or no thought at all. It can't really be avoided. It might be an open question whether one should do something about unjustified beliefs one notices one holds. And I don't think there's anything inherently wrong with asserting an unjustified belief.

Of course, I'm even using 'unjustified' above tentatively - it would be better to say "insufficiently justified for the context" in which case the problem goes away - certainly seeing what looks like a flower is sufficient justification for the belief that there is a flower, if nothing turns on it.

Not sure which sort of case Roko's is, though.