Sometimes a work of art takes just as much effort to understand as a difficult book.
But should it? I did an art appreciation course some years ago and the tutor said that a work of art should have many layers, and that it should have the capacity to engage you on first glance and thereby encourage you to look further and to explore its deeper layers.
However the implications of Gloryanny's post that more or less suggests that unless you have done an art appreciation course or have a qualification in fine art, you are incapable of making a reasoned response to a piece of art, modern or not, shows such breathtaking intellectual arrogance, that it rather confirms some people's suspicions that modern art is a big con.
If you look back, in many periods artworks held hints and layers that were understandable only to the highly educated or the cognoscenti, modern art, whatever the period it was modern, has always been subject tothe intellectual snobbery of the 'elite' who pride themselves on being the only ones who really understand it. But at least in the past could be admired by anyone glorious picture, or the use of colour and texture was instantly pleasing to the eye and drew people in. The purpose of some 'modern art' seems to be to exclude people.
The same applies to literature, just because someone has difficulty reading a book does not mean that they do not recognise it is good literature. I studied Middlemarch at A Level, I struggled with the book at the time. I have read it several times since and finally did an extra-mural course at Oxford and now feel I can now engage with the book, but at no time did I doubt it was great literature. I can say the same of several other books. We all know the story of the Emperors New Clothes
But reactions to art - of any kind - are subjective. Look backwards and you can see artists, authors, composers, whose work was highly regarded in their time, but have since sunk without trace, some justifiably, some probably not.
Modern art has yet to stand the test of time, which will begin to seperate the meritous from the meritricious.