"Ideological" as a category of legal analysis in McDonald v. Longley -- the need for a definition

I am mulling the new Fifth Circuit case McDonald v. Longley, which has held the requirement of membership in the State Bar of Texas as a condition to practicing law to be unconstitutional under the rubric of freedom of association. I intend to present a deep analysis of this decision--particularly illuminated by the history of the organized bar in Texas--in future posts, but for now I offer this observation: the appellate court is using a term not defined in the premier legal dictionary, Black's Law Dictionary (11th ed., 2019).

In the first sentence and then a dozen times more in this new case, the Fifth Circuit uses the adjective "ideological," and it also uses the adverbial form three times and the noun once. Mostly the court uses the adjective in the catchphrase "political and ideological" (sometimes with "or" in the middle); but several times "ideological" used alone. Because the court found that the State Bar of Texas engages in certain activities that, albeit limited, constitute "ideological" activity, the mandatory nature of the State Bar is held to be unconstitutional.

"Political" is defined in that dictionary, as is "politics," but not "ideological." It does define the catchphrase "ideological aggression" by referring to its definition of "propaganda." But that does not help define "ideology" or ideological." 

Perhaps particularly because I grew up in the fifties and sixties when "ideological" was often used as a term of opprobrium meaning, more or less, that a person's beliefs or activities somehow pertained to Communism(!) and because I have not previously conceived of "ideological" as a category of legal analysis, I am craving a good definition for today.

I checked the online Oxford English Dictionary, and of three definitions, this one seems germane (another adjective used repeatedly in the McDonald opinion): "Of or relating to a political, economic, or other ideology . . . ; based on a principle or set of unshakeable beliefs." 

And "ideology," it says, means "A systematic scheme of ideas, usually relating to politics, economics, or society and forming the basis of action or policy; a set of beliefs governing conduct. Also: the forming or holding of such a scheme of ideas." 

Returning to the McDonald case, the Fifth Circuit undoubtedly used the subject term because the Supreme Court had done so in Keller v. State Bar of Cal., 496 U.S. 1 (1990). Chief Justice William Rehnquist  there wrote: "[based on] the State's interest in regulating the legal profession and improving the quality of legal services[, t]he State Bar may therefore constitutionally fund activities germane to those goals out of the mandatory dues of all members. It may not, however, in such manner fund activities of an ideological nature which fall outside of those areas of activity. The difficult question, of course, is to define the latter class of activities." (emphasis added)

Rehnquist did not define "ideological," saying the line "will not always be easy to discern. But the extreme ends of the spectrum are clear: Compulsory dues may not be expended to endorse or advance a gun control or nuclear weapons freeze initiative; at the other end of the spectrum petitioners have no valid constitutional objection to their compulsory dues being spent for activities connected with disciplining members of the Bar or proposing ethical codes for the profession."

My immediate conclusion is that it would be helpful to the courts and to the bar to have a definition of "ideological" (and its noun form) in Black's.