I find that sometimes(not always, by any means) people born into a religion never actually look at the texts; they just kinda go by what Ma or Pa said/did. Or, they just use it as a cultural label and assume whatever their culture pushes is what the religion pushes(I think you see a lot of that in the US).
This is one reason that I cannot judge a religion by the actions of its adherents.
A lot of religious individuals are ignorant of what their religion actually teaches. By listening to Hamza Yusuf, for instance, I learned that most Muslims don’t read Qur’an or any other texts, and that so many Muslims follow what they hear from young men who aren’t even ulema. Moreover, when it comes to Hinduism, I’ve read that most Hindus in India don’t know things that those of us from the West who embraced Hinduism know well. Further, I’ve heard a well known Sikh explain that Sikhs in general get much of their information about Sikhi from unreliable sources rather than their Guru. How could one judge almost any religion then by the behavior of its adherents if the adherents don’t even understand the religion properly?
One more reason that I cannot judge a religion by its adherents is that human beings are incredibly fallible entities. From my perspective, judging a religion by its adherents requires one to assume that the adherents not only understand the religion properly but also that they practice it correctly and faithfully during every waking moment. Most of us fail to do many things correctly and faithfully, so how could we expect a community to somehow do much better but with respect to religion?