Appeal to ridicule (reductio ad ridiculum)
Comparing belief in black holes to belief in 'other space oddities' (unspecified but presumably including highly improbable or even impossible things) is not a good argument. Logically it has no cogency. It is merely an appeal to ridicule, which counts as a fallacy on most reckonings. Compare : 'If you believe the Chinese economy will crash, you'll believe there are fairies at the bottom of the garden'. Laughter all round but no cogent argument for the inference.
The ridicule is made worse in this case because (1) 'space oddity' is a vague and unspecific term) and (2) there is no reason why a black hole should not be a 'space oddity' in some distinct respect and yet exist. After all in a black hole the normal rules for behaviour in space/time do not apply. A black hole is a singularity. That makes it a 'space oddity' in a distinct and scientifically respectable sense but counts for nothing as an argument against the existence of black holes.
To put the point another way ...
'Space oddity' is too imprecise a term to argue much over. There is a singularity about black holes &, because of this, for a considerable time many physicists did not believe in their existence. In this sense they are 'space oddities'. My point is that being a space oddity, if we have to use this term, is no argument against a black hole's existence. Believing in a black holes does not commit one to believing in the existence of the ether, 108 dimensions of space/ time, or the moon's being made of green cheese - other space oddities of the sort your ridiculer presumably has in mind.