Not easy to 'comment'
One the one hand, some might say that the alternative for the cockroach would most likely be to be squashed by a slipper, i.e. killed, so it doesn't matter.
On the other hand, there is a difference between killing a pest and doing things to it which might be seen as showing a lack of respect and humanity to a living thing. It is perhaps not merely what is being done to the insect that is of concern, but also the impact on the mind of the person who is doing it. Since these experiments are not in any way scientific, the real reason for people conducting them, which may include likely varying degrees of sadism, may not be something that should be encouraged.
If many people are enabled or encouraged to conduct such experiments on insects, a small proportion of them might also eventually graduate to bigger subjects.
Doctor Mengele used to conduct vivisection experiments on death camp inmates and could surely have used the argument that they were up for the chop anyway, so it didn't matter - what with the people in question being non-Aryans and thus equivalent to rats and cockroaches in his country's mindset at the time.