There are rights and concerns that override the obligation not to kill for almost everyone, and those rights and concerns are dependent in part on the characteristics of what is being killed.If it is "very important rights" that can override the obligation not to kill, that just means there are other rules in your moral view that are of higher priority.
For instance, the concern for my own sustenance overrides my obligation not to kill plants. It does not override my obligation not to kill animals, but other people do consider it to override that too.
What changes from person to person is not actually an adherence to an absolute rule or not-- the only people who adhere absolutely to a rule of no-killing are a subset of fruitarians. What changes from person to person is: 1) which concerns are weighed against it; and 2) the characteristics of the object. You have determined that sharing a species is a characteristic that overrides quality of life and various other concerns (but presumably not self-defence or some others). I have determined that more relevant characteristics are the capacity for its own interests, preferences, and suffering-- characteristics that encompass a lot of animals, but do not encompass clumps of unaware cells that happen to share my species.
((Not attempting to speak for Seanchaidh here ofc, just giving my two cents as I was involved earlier))