The case for believing that all religions are the same often is supported by the claim that all major religions teach the Golden Rule. However, I think it’s notable there are differences in the way this Golden Rule is phrased. Some phrase it as “Do unto others as you would have them do unto you,” and some phrase it as a compound negative–“Do not do unto others as you would not have them do unto you.”
The interesting correlation I see is that religions with a positive Golden Rule tend to be proselytizing religions. “I am glad that I was converted; therefore, I should try to convert others.” Religions with a negative Golden Rule tend to be non-proselytizing. “I wouldn’t like it if someone tried to convert me away, so I shouldn’t try to convert others away from their religions.”
The only anomaly in this case (with the versions taken from here) is Jainism, which is a non-proselytizing religion that has a positive Golden Rule.
As I said in my previous post, what’s interesting about different religions is the differences in what they say about compassion. If someone is on the wrong path, to what extent is it compassionate to correct them, and to what extent is it compassionate to let them be? The different religions of the world, and their differences, ensure that we’ll keep looking at this issue. We won’t all come to the same answer, and that’s for the best.