A pathogenic organism can have subtle differences in its surface antigens due to imperfect manufacture or because of damage. It makes sense to have a little flexibility in the bind properties of an antibody. However, sometimes an antibody can cross react with an antigen on an entirely innocuous structure including our own self antigens. Only one antigen will fit into an antibody receptor cup fit absolutely perfectly. Each antibody receptor might accept other antigens that look similar to the one it was designed for, but if the fit is not good then most likely the binding between antibody and antigen will be weak.
Any inflammatory reaction is a destructive process.
The intention of inflammation is to break down bacteria or cells or whatever the perceived threat is to render it harmless to the body. This destruction and breakdown of the target creates a lot of debris. The bacteria or cell fragments have to be removed from the tissue and blood stream otherwise over time they will increase in concentration and basically gum up the works. In addition, these fragments may still be antigenic. For as long as they remain in the system they have the ability to stimulate the immune system.