For the sake of simplicity, in this post I will assume that given a specific concrete question, person1 either agrees, or disagrees with a person2, and, similarly, person1 either agrees or disagrees with a specific point in a movement's program. Then "person1 agreeing with someone about something" is a function that outputs either 0 or 1. The arguments of this function are (person1, person2, question/statement) or (person1, movement, question/statement). Now, given person1 and person2 (or person1 and movement) one can take a list of questions/statements, and calculate the percentage of agreement for this questionnaire. If a movement has a list of statements (in other words, a list of yes/no questions) "what this movement is all about", then we can similarly calculate person1's percentage of agreement with this movement.
For the sake of simplicity, I am talking specifically about concrete and specific yes/no questions and statements. In this case, very broad statements should be understood as being shorthands for long lists of specific statements (i.e. "X should always do Y" should be understood as a shorthand for the list "X should do Y in a situation1", "X should do Y in a situation2", etc.).
The point I am trying to make is this. The length of these lists of questions/statements is usually not very well defined and you can increase the percentage of agreements by stuffing the list with questions and statements with near universal agreement (common sense statements) or you can decrease the percentage of agreement by cutting uncontroversial questions out from the list ("this is common sense, you don't need a movement for that"). And when you lengthen or shorten the list of question, various things happen.
It is my impression that if a person identifies with a movement, then they are likely to see common sense as a part of the program of the movement. The unwritten list of questions and statements is long and it is very easy to get high percentage of agreement. If a person doesn't identify with a movement, they are unlikely to see common sense as a part of "what this movement is all about" (they don't think they need movement1 where common sense is enough). To them, the things movement1 is all about are the things where the movement1 differs from common sense or tries to go beyond common sense. In this case, the list of questions is much shorter since uncontroversial common sense questions aren't included in the list.
For the sake of simplicity, let's assume that you cannot easily drop controversial questions out of the list, as it is beyond the scope of this model.
If, for some reason, a person wants to see himself/herself as agreeing with a movement, but, at the same time, does not want to change their yes/no answers to specific questions, they may try to lengthen the list by including many "easy questions" which are hardly unique to the movement. If a person's views about a movement are unfavourable, then in their minds it is the controversial questions that the movement is all about, in their minds the list is much shorter.
On the other side of the coin, movements often try to attract new people by lengthening their lists by stuffing them with various slogans and platitutes and claiming that they are very important part to their identity.
Suppose person A says that he/she 90% agrees with movement1, and person B says that he/she 40% percent agrees with it. As you can see, it does not necessarily mean that they must disagree about any given concrete question. It is possible that their respective lists of questions are simply different in length, that is, their opinions whether certain common sense statements belong to the discussion about movement1 are different.
However, if you are designing a list for a movement, you cannot add just any question you want to any given list. It is my impression that there must be at least some (real or perceived) disagreement with someone (who is again, real or perceived) about it, otherwise people will not think about that question as a part of your movement. For example, you cannot add support for the law of gravity to the list of things your movement supports and expect that people will actually include this question calculating their percentage of agreements.
Threats, both real and imaginary, are often helpful for movements, because they enable them to add uncontroversial questions and portray them as controversial, thus making it easier to reach high percentages of agreement with people.
If a question stops being controversial over the time, it becomes rarely included into the people's lists of questions, which might lead to decreases in their respective percentages of agreement with movement1, even if it was movement1's supported position that prevailed and became common sense. In this case, movement1 may try to talk a lot about the past and emphasize the small remnants (again, both real or imaginary) of dissent. If a movement no longer has positions that haven't dropped out of the list, it probably stops being considered a movement. At the same time, movements (theoretically) try to win and making your position common sense is a victory in some sense.
It is interesting to think what dynamics this might lead to. It seems that if most movement's positions are becoming common sense, perhaps it has to introduce controversial statements in order to stay a movement. If a movement is too much disagreed with, it may either have to try to distance themselves from controversial questions somehow, or try to stuff their list with a lot of statements that aren't very controversial by trying to emphasize that common sense is part of their identity. Another interesting dynamics might be introduced by geography, where different questions belong to common sense or are controversial in different parts of the world, yet those different parts know about each other.
To sum up, the lists of questions/statements are not strictly defined. People who identify with a movement (but not necessarily agree with every statement) seem to be likely to think of the list as much longer and contain a lot of common sense statements. People who perceive themselves as outsiders are likely to think that uncontroversial common sense statements do not belong to the list.
(feel free to correct mistakes, both grammatical and those related to the content of the post itself, advice on the presentation itself, comments about what was unclear are also appreciated)