I think this is a very good question.
I do not own any knives totally designated for knife fighting. At my age and knowing what I know now, learning where the exits are is more of a realistic education. Due to a knife's limited range and the exposure to blood borne pathogens, I'd throw a chair at the aggressor first.
However, there are many great fighting knives, and I think that the sport of collecting such implements is a valid persuit. For example, I collect PEZ dispensers, but I never eat the candy. Several of my handguns were designed for 'combat,' that is, single stackers for running barricades in IPSC.
I had read the history of some Randall designs. The story goes that a guy who really was in fights went to a cutler to have a design improved. Ernie designed the CQC6, which really went to Desert Storm. Bill Bagwell makes the best Bowies I've seen.
In any hobby or collection, I believe "collecting for the sake of collecting" is valid. You need not explain your intent to anyone.