Opera is extreme above all other genres. I know this from a few memorable performances I have seen/heard/felt. In each case a magnificently complex production led up to a moment in the third act when the heroine (soprano) could not control her voice and made an uninhibited animal sound--fleeting but oh so powerful. It happened once at the Met in Traviata, once at the NYCity Opera in Handel's Alcina; in a recent Mannes College production of Don Giovanni it was baritone Ricardo Rivera who allowed it to happen.
Allowing it to happen is a function, first of all, of inspired composition: the composer knows the voice and writes into the part the difference between vulnerability and sheer confidence. Masterful vocal writing does not get better than in the hands of Verdi, Handel, and Mozart.
Today I realized that I have never seen a Schubert opera. I wonder why? Who is afraid of them? Is it an issue of style? (Mozart's Idomineo was not performed until recently, after the revival of interest in early music, when people realized that it was essentially a Baroque opera.)