just like with midsommar, so too in 28 years later, i see many people misrepresenting the island community as a good an moral safe haven compared to the wilderness &, say, the lawlessness and cruelty of Jimmy Crystal's gang
but that's wrong. the island community is just another expression of the backward, reactionary extremism humans cling to when they think they're being threatened by something they perceive as 'other'
for instance, in the montage of the community getting ready to welcome back jamie and spike, which is framed as a joyous communal moment, you clearly see the exacerbation of religion and love of "country", the picture of a queen of england that's just a ghost ruling over a wasteland. the women have clearcut roles of service, they prepare the meals, teach, decorate the communal spaces, make pretty signs for their tryumphant men coming home; it's the boys who train in archery, who are taught to fight and protect. that's not idyllic. that's a commentary on how insular communities, especially in the face of attacks by 'outsiders', tend to close themselves further and reinforce very archaic ideals of how a better society is to be reimagined. they have one encounter with the doctor, deem him 'odd' and refuse to interact with him for over 15 years (rejection of science: however positive or negative you deem fiennes' character to be, the point still stands), not even when a clearly disabled person from the community who is in a lot of pain (spike's mother) and close to death needs help.
and this kind of life is the kind of life spike rejects. he does not reject his father, he just accepts him as being a flawed person who did his best and had clear failings but not necessarily malicious ones. spike sees the possibility of a different way of life, and that's what he hopes to chase.