Political movements may be rather various. They may have bright slogans; they can proclaim ideas with which it's hard to argue (for example, that poverty and injustice are bad, and protection of environment is good); they may be supported by celebrities (though to be a celebrity still doesn't mean to be clever); there may be really dedicated and self-sacrificing people among their activists, and really unattractive persons and organizations among their opponents. But still--how to distinguish that despite of all this they are selling you a load of crap?
Here are the most typical signs. Each of them separately doesn't give a complete guarantee yet, but is a serious reason, at least, to become more sharply alert. And their combination turns alert into assurance.
1. The movement declares that it expresses the will of overwhelming majority. Especially if actually only hundreds and thousands, not any way millions, participate in its actions . However, a really numerous movement speaking in the name of "all people" is even more dangerous.
2. The participants of the movement resort to violence first. Especially if the violence is directed not against the force structures but against peaceful civilians and their property (breaking of show-windows, arson of cars and so on, up to drawing graffiti on the walls of private houses), and also if serious hindrances are created to the same civilians in other ways (for example, long blocking of public roads, hindering the operation of institutions necessary for general public). It is necessary, of course, to take into account the possibility of provocations--but in such cases it is especially important how the leaders and ordinary participants of the movement react to these provocations, whether they take drastic and immediate measures to suppress them.
3. The movement has no constructive program. The majority of slogans are "contra", not "pro", and those which are still "pro" are just indistinct good wishes (sometimes, however, even not so good) not supported by any concrete mechanisms of their realizations. NB: appeals like "to raise taxes", "to establish protecting customs", "to increase social benefits" and so on, without a serious professional analysis of consequences of such actions, cannot be considered as a constructive program .
4. The movement consists almost exclusively of the youth--or, more general, there are practically no professionally successful persons among the participants of the movement . It doesn't mean at all that young people are always silly, ignorant and irresponsible--but if they are not supported by anybody more skilled and solid, by those who have proved their intellect and abilities by real work and practical success, and if the only older supporters of the movement are "eternal students", welfare recipients and so on, it is already an important sign. Besides, this testifies once again the absence of a constructive program of the movement--there is just nobody who could develop it.
5. The participants of the movement are ready to hold mass-meetings days, weeks, months long, to live in tents in streets and squares. The people who do something really useful simply don't have time for that. (It should be noted, however, that this point is true only for democratic countries, where free press and fair elections exist; but in the countries having big troubles in these aspects, the protest actions lasting for many days may be indeed the only way out from a critical situation.)
6. The participants of the movement are slovenly, and on the place of their actions there is a lot of garbage.
7. The ordinary participants of the movement have no opinion of their own and only refer to their leaders; at an attempt of a well-grounded dispute with them, they demonstrate ignorance and/or aggression.
8. The participants of the movement actively dislike journalists if they aren't sure that the latter represent mass-media supporting the movement.
9. The movement is supported by anti-semites, whether they are frank nazis or any kinds of "fighters for the freedom of Palestine" and "opponents of zionism". It doesn't mean that a single such person can discredit a good idea--but grouping of such characters around the movement, even if they formally are not a part of it, should at least make alert. Certainly, here it is necessary to consider the possibility of provocations, too .
While making this list I abstracted from my own political views as much as possible. But in the end I nevertheless cannot abstain from making an obvious conclusion: whether it is surprising that these signs are the most typical for the left movements?