The INFP is almost a cosmical type.
Thus, the distinction between a good cause and a bad cause is not based on any objective criteria (that is the business of Thinking!) but based on what 'feels good', hence, whatever agrees with the INFP's instincts is good and what does not, is not.
There is very little by way of sincerity with regard to how this type functions, contrary to what appears to be the case on a very superficial level. The INFP is driven to please others in order to be in harmony with them.
For this reason, the INFP engages the emotions of others for self-serving ends, strictly to receive positive emotion in return.
One may be attracted to the INFP based on what they appear to be on the surface, specifically, deep and highly emotionally sensitive. Deep? There is depth of sentiment no doubt, but can we regard this as legitimate depth as such a quality is associated with a virtue of character? Not at all, as the causes the INFP fights for are not deep at all, because the causes are determined by Thinking (as Thinking decides what the world is) because Thinking is very primitive and subordinate to the impulses of the INFP, the causes this type feels passionate about are often unremarkable at best, and opprobrious at worst. The 'INFPs versus the ESTJs' myspace group is the case in point. One may ask, what about the INFPs who fight for the end of war, getting the homeless off the streets, or raising the salaries?
Two likely answers, either the INFPs in question have developed their Thinking (very few do, hence, the ones we have in mind here are not representative of this type) or what is much more common is, simply acting out on their Feeling which relentlessly urge them to seek approbation from others. Merely identified with the cause that others value and spoke up in their endeavor to get praise from others.
In other words, they were not fighting for anything noble, they did not even know what they were doing, they were merely acting out on their impulse to try to be liked by others, as they usually do. (The nature of Feeling strives to generate positive sentiment, therefore longs for harmony with others).
-Because point one is the case, the INFP is unable to have a clear view of who they are and how they ought to live their lives, and as a result lack a backbone. Their life tends to be an incessant overflow of torrential, self-serving and in almost all notable respects vulgar passion.
*This post was about applied typology, not pure typology. In other words, it is not about the unconscious tendencies of the INFP, but about how a typical INFP tends to be. The only exception to the above is the case of the INFP with a well developed Thinking faculty which is indeed rare.