It seems Soma does not want her mother to kill the cockroach because she opposes killing insects unnecessarily, even if they are unpleasant pests. Some possible reasons Soma may have opposed killing the cockroach:
1. She believes in compassion for all living creatures, even insects. She thinks there are humane ways to get rid of cockroaches rather than killing them.
2. She thinks cockroaches have a right to life too, as long as they are not directly harming humans or threatening health and safety. Killing them as a first resort is unjustified.
3. She may think cockroaches serve some purpose in the ecosystem and food chain, so they should not be exterminated casually.
4. She could see the cockroach as a fellow living being deserving of mercy and a chance to live, rather than an automatic target for killing.
In contrast, the mother likely opposed Soma's view because:
1. She finds cockroaches disgusting and sees killing them as the only reasonable solution to get rid of an infestation.
2. She thinks Soma is being too compassionate towards useless vermin at the cost of hygiene and practicality.
3. She may see it as Soma being too sentimental or foolishly opposed to the only effective method of dealing with cockroaches.
4. There could be a difference in viewpoint and tolerance for insects between the generations. The mother's perspective may be more pragmatic while Soma's is more ethical.
Does this help explain the possible reasons for the difference in perspectives? Let me know if you need any clarification.