As a Platonist I want to understand the purpose or objective (teleos) of any thing. Unless one knows why one is doing something (what it is one wants to achieve) one can hardly set about doing so. Moreover, for one to have an objective, one must think that this is of some benefit, or else one wouldn't be motivated to attain it.
Again, as a Platonist, I want to promote justice (that is harmony, freedom, wholesomeness and friendship) so as to facilitate life and happiness in everything that I do. I think that the support of life and joy of living is the basic value and the benefit that is every human being's deepest desire. Plato argued that it was everyone's business to live justly and to promote justice - according to their position in life, expertise and trade.
So, as a Platonist, I believe that Art should - one way or another - encourage both its creators and its admirers to become better people: kinder, gentler - altogether more appreciative of what is good, constructive and wholesome in the world and altogether more depreciative of what is vicious, destructive and morbid.
Obtaining a reaction which makes people better is a good objective. So, exposing bigotry, hypocrisy, foolishness, cruelty, cowardice, tyranny or whatever is good; equally manifesting love, peace, bravery, consideration or whatever is good. Offering people comfort and encouragement in distress is good.
Obtaining a reaction which "depraves and corrupts" people (and I don't take this phrase to be mainly to do with sex - people are depraved and corrupted in much more important aspects of their lives than this!) is a bad objective.
A few years ago, I saw a play at the Edinburgh Fringe. I forget the name. It was a superb production. Acted, directed and produced with singular skill. It was, however, a despicable piece of "Art". I don't remember the exact details, but its theme was - more or less - that good was the same as evil. This is a lie and exactly the kind of message that "depraves and corrupts" at the deepest level.
Some "boundaries" are mere convention. Some of these should be blurred in order to free people to discover their own integrity. Sexual boundaries are a case in point here. On the other hand, some conventions should never be blurred - the obvious example being which side of the road one drives on: that boundary it is very dangerous and foolish to "blur".
Some "boundaries" are not conventional at all. The obvious one in art is between "beauty" and "ugliness". Now, "beauty" is multiform, and what one person can see as beautiful another person may have no regard for at all. This is fine, and it can be a worthy endeavour to explore the nature of beauty and push boundaries. What is not fine is to blur the boundary between the ideas of "beauty" and "ugliness" and to say the "ugliness is beautiful" or that Art is just as concerned with promoting ugliness as with promoting beauty.
Sometimes it is valuable to represent ugliness - if one has a noble purpose in doing so - but to represent ugliness for its own sake: just to shock, or worse to suggest that ugliness is just as "valid" as beauty and so to devalue beauty (while doing nothing to improve the condition of ugliness) is truly wicked.
A true artist is concerned with themselves and with their Art; not with the effect that it has on others - in the sense of whether or not they receive acclamation or money. If an artist concentrates on producing work which speaks to themselves of what is valuable and beautiful and worth-while (perhaps by exemplifying what is not so in order to produce a critical counter-reaction) then that should be enough. If they have done work which is good, it will be recognised for what it is by those who are ready to receive its message.
It seems to me that it is the (self-)publicist who is primarily concerned with the "effectiveness" of their endeavours, not the Artist. The true Artist would be happy to perfect their Art in private, with no prospect of anyone else ever appreciating it: just for the joy of creating it and appreciating it themselves.