If something is fine before a given change, and people prefer how it is to how the change would make it, though — well, there's a guideline on WP that explains it pretty well, in my opinion: "Believing that you have a valid point does not confer upon you the right to act as though your point must be accepted by the community when you have been told that it is not accepted." It also sounds like it's becoming a chicken-and-egg issue, if you don't want to discuss proposals because you think they'll be opposed, while some of the people who've opposed some of your recent proposals seem to be unhappy with your tendency to make mass changes without consensus.
In this case, I think it's logical for the parameter supplied to {{head}} to be singular like the part of speech itself and the part-of-speech header (cat is a "noun", not a "nouns"). Your post on WT:NFE about bringing {{head}} "in line with the catN= parameters, which already take the name in plural form" suggests that you think that is more logical, so in the absence of others' comments, I suppose our opinions on what is logical may cancel out... though I'm guessing "catN=" is less common than either instances of {{head}} or part-of-speech headers, since I can't think of what "catN=" is. (I.e., I'm guessing there are more singular things for {{head}} to align with than plural things.) Typing out the plural also (a) takes more keystrokes (DCDuring's perennial concern, and increasingly a concern of mine as well), and (b) requires relearning, since people are accustomed to putting the part of speech into {{head}} in the singular.
You might say that isn't a reason not to change existing entries and templates, but to that I'd say: (a) there's also no reason to change the existing templates and entries (and it's making changes, rather than not making them, which requires justification and consensus); and (b) I'm well aware that when changes are made en masse to deprecate something from existing entries and templates, there are sooner or later efforts to ban the thing from new entries, on the grounds that "there are only a few entries that use this anymore".