There has always been bad grammar too. Also forms that were once fully correct can become incorrect. I try (with mixed success) to stick with whatever pedantic people have claimed was the rule for the last 100 years or so.

Using "less" instead of "fewer" is not very damaging. But when style guides consistently say "you can do this, or that, it's up to you" then the language just becomes more ambiguous and opaque than it already is.

A good example is allowing "phenomena" as a singular. This just creates ambiguity. Now if people had started to use "phenomenons" as a plural, there might be a reason to rubber-stamp it.