Why social animals attack odd members of their own group?
Persecution is not a term often used in zoology, compared for example to the notion of social exclusion and hierarchy disputes/social animal hierarchy. That is because humans incarcerate animals which would otherwise flee to safe distance from the group if they are attacked. Wild Mammals, birds, fish, other animals with free movement can normally get safe distance from an aggressive group in order to be safe from persecution.
Fish and insects/island animals sometimes have restricted ranges, and &quot;social exclusion of a mutant&quot; - studies are difficult to find and perhaps won't give masses of information to know why it happens, for categorization and prevalence of different reasons.
I found only one research on social aggression based on appearance:Aggressive biases towards similarly coloured males in Lake Malawi.
Useful related terms for further research for your question are i.e.:

&quot;social exclusion mutants traits aggression&quot;
&quot;social exclusion zoology&quot;
&quot;social exclusion injury zoology&quot;
&quot;social exclusion zoology mutation&quot;
&quot;hyerarchy disputes appearance zoology&quot;

It's an interesting notion for research that you have found, for which a lot can be written, because it gives a complex range of potential reasons for the given behaviour: warding off a contagious individual, warding off a tribe from far away that could displace the current group, inability for the brain to average the mutant's appearance to associate with it, habituation of species to a type of social companion since their birth (i.e. birds sometimes think they are humans)
And so a research requires a broad understanding of juvenile establishment of appearance recognition of other individuals of the group, i.e. where humans search for an average appearance compared to the social group, and chimps recognize close relatives and mate with the most distant, chickens can adopt humans... and animal behaviour towards an ill individual, it's difficult and takes a while to gather actual sci documents for.
When you have found all the closest related research, the given write up would be very fascinating!!! i hope you can search the given topics and give a summary of some previous examples of vaguely related research.