Their rationale as such is understandable. Behind the word 買う, there is a metaphor that you obtain something originally belongs to the other. 批判・非難・苦情 that they mentioned are things which are only actualized in interaction between people, and not what occurs inside the opponent's mind alone.
However, in the background of those "frequently misused" words is also a fact that they are supported by and often inseparable with a certain emotion. What is more, considering that words like 反発, 不評 or 同情 (which I think okay for them) are normally used for both the inner feeling and the outer expression, it is a bit too cognitively demanding to require a sharp line between these two in reality.
So, I personally do not feel much stretch seeing 批判を買う, but some people might feel unnaturalness for the reason above. 明鏡 indeed has a reputation being on the prescriptivist side in native speakers' eyes, and that is not necessarily bad as a dictionary.
In most times firmer words you want with the intended nuances of 批判／非難を買う are ～を呼ぶ／浴びる, and 苦情をもらう.
Querying over BCCWJ, you'll find one appearance of 批判を買う:
as well as some counterexamples when you try to apply the rule rigorously, such as:
忌避 implies the action of avoiding something (though it's not an "active" action).
But the most problematic one IMO is 失笑を買う, that appears as often as 不評を買う (15 times) and among them are the works of relatively conservative authors.
Note: the spelling is his style; not an old work
失笑 prescriptively needs to be an expressed action (though confirmed by the authority for an unrelated reason), thus we cannot have it both ways.