Fair points, but I think youthful idealism is a beautiful thing, and the tragedy of life - captured powerfully because of Merrily's reverse structure - is that the world, which is "us" and all our weaknesses we bring - plays havoc with our best intentions. The truly bold, who shed the shackles of human compromise, are usually arrested, removed, or lionised much later as saints.
I recall the line from Anyone Can Whistle in which Hapgood says he is not only an idealist, but a "practising" one.
They're very rare, which is the tragedy of the human condition. I think Merrily, told backwards, makes us especially aware of the tragedy. Personally, I don't mind sitting in a theatre studying unlikeable people when there is a moral purpose to it; I'm not all that fond of Oedipus, that arrogant sod; or that hormone-crazed Romeo, the fool; or Henry-bloody-Higgins, that egotistical power-hungry creep; and as for that narrow-minded Nellie Forbush, who grows more dislikeable as the show goes on, rather than the reverse (until the end....) - mind you, as for that overbearing lover she's got ........ or that Cable character .... or - or - Bloody Mary, a mother who does that !!!
Sorry, where was I? As I say, better to study the unlikeable in a purposeful, artificial space - it's slightly better than having to put up with them in real life!