Most of the regular contributors to this site would probably agree with Anton in principle that the newcomers to this site should feel welcome. His post, however, makes a couple of assumptions that are debatable.
First, Anton seems to assume that everybody who posts one or two things on this site is eager to learn its customs and become a long-term contributor to it. That does not seem to be the case. Trolls and spammers have already been mentioned in the comments, but there is a much larger number of those who are used to participating, and who enjoy participating, in the sites of some different kind, and who post something here in the mistaken belief that this is yet another site of that kind. As soon as they realise that this is not the case, they, understandably, lose interest in it. Are they newcomers, in the sense that is relevant here? Incidentally, the mistakes of this kind can be easily avoided by 'lurking' on the site for a little while, and familiarising oneself with its nature, before posting something.
Second, Anton, as many other, but by no means all, regular contributors to this site regards providing feedback to the poster as the primary function of voting. The proposal that the newcomers should not be downvoted is then based on an analogy with the lenience that a teacher may display in grading beginning students. Voting, however, also has another function: it is a signal to those who may come across the post later of how worthy of their attention it is. It is, at least, debatable which of these two functions is more important. The site is already designed so as to soften the impact of the downvotes on the poster who receives them, in that the downvotes have only one fifth of the influence on the poster's reputation that the upvotes have, while having the same weight in affecting the displayed net votes.
Finally, if anything on this site deserves to be characterised as 'mute and spiteful negativity' that discourages newcomers, it is not downvoting, but the closing of questions with the 'reasons' that are bewilderingly unrelated to the question. 'Mute' downvoting seems more respectful to the questioner, and may feel much less like stonewalling, than the blue banner that is not quite mute, but instead speaks in an Alice-in-the-Wonderland manner. Paradoxically, the main reason why the closing banners so often confusingly obscure the real reasons for closing is that those who formulated them were trying too hard to be polite, encouraging, and euphemistic; the standard formulations of the reasons for closing that were in use some years ago were more blunt, but their clarity may have made them, on the whole, less frustrating to the questioners than the current ones are.
My feeling is therefore that downvoting of newcomers with reputations below some small and yet to be decided threshold should not be possible.I was also going to point out that reputation is bad measure of "newcomerness" but chose to interpret that as just some measure instead of reputation specifically.