TBH I disagree. In some fields it has become something of a convention, especially when the thing you're pluralizing is a variable or some other mathematical expression. For example I might write $x_1,x_2,...,x_n$, and then refer to the sequence as "the $x$'s". Happens all the time in professional journals by authors who know very well what the prescriptive rules of written English are. It is just easier to read this way.