The subjunctive case is out of fashion, and has been so for a long time. Naturally, therefore, I espouse it.
That's not really the case (get it, the case?). What I mean is that I do espouse it (the subjunctive case), but not "naturally", which implies I would promote something simply because it is archaic or out of fashion. I try to limit to some extent the windmill-tilting in which I engage.
According to Wikipedia, to which I am indebted for some of the substance of this article (and could have been indebted for so much more, count your lucky stars), subjunctive is really a mood rather than a case, and, not only that, but a mood with an alias or two, a/k/a conjunctive, a/k/a conjunctive mood.
I'm not going to delve deeply into the grammar underlying mood in place of case or even, by any means, all the information concerning subjunctive be it case or mood or conjunctive (but let's not conjecture), but I will point out that this particular mood exists in a multitude of languages. Why? Because it expresses what could be, what might have been, or what should be. Contrast this with the plain and unadorned indicative, which states what is, what was, or what will be:
Indicative if I was if I knew as it was powers that are if he comes
Subjunctive if I were had I known as it were powers that be should he come
Bottom line (in more ways than one):
It is not wrong to be indicative in place of subjunctive. But it may not be as elegant.