Ι think there is a reason why this type of discussion usually goes round and round in circles until it eventually hits a brick wall. The problem is that many people actually expect someone in a public forum to summarise in 2 paragraphs for them what is art, what isnt, that there is no art, or all art is subjective or something like that, and once this is done the problem is solved forever and they will not have to worry about it anymore. Well, its just not that simple.
I think this type of discussion can be meaningful but only between likeminded people who have some sort of common background, otherwise it just gets too chaotic.