Why do most biologists believe that true commensalism does not exist?

the relationships are probably mutual or parasitic
animals of the same species rarely compete with one another
animals of different species usually do not like to work together
an ecosystem usually has more parasites than hosts

the relationships are probably mutual or parasitic

Explanation:

The argument of most scientists when it comes to commensalism is that the likelihood of a relationship between two different organisms, where one of the organisms to be completely unaffected is low. They propose that their relationship, although not obvious, is more likely to be mutualistic or parasitic at best.