I think judgmentalism is making judgments without understanding all the factors that contribute to what is being judged and, thus, judging incorrectly to one degree or another. When it comes to judging people themselves (as opposed to their actions), we rarely or never understand all of the factors completely, so we are commanded not to judge them (assign them an eternal reward or punishment).
I think judgmentalism is a pretty good way to phrase the opposite of charity, although most people don't compare them directly.
Charity suffereth long, and is kind; charity envieth not; charity vaunteth not itself, is not puffed up, doth not behave itself unseemly, seeketh not her own, is not easily provoked, thinketh no evil; rejoiceth not in iniquity, but rejoiceth in the truth; beareth all things, believeth all things, hopeth all things, endureth all things. (1 Corinthians 13:4-7)
Judgmentalism does none of that.
Unfortunately, however, it is one of the single biggest "natural" instincts we have.