[sc_rufctr]

In the case about Manson and his new wife... There is a very small percentage of women world wide who are attracted to very dangerous men.
(much less than .01% but world wide that's equates to many thousands)
The worse these men are the more attractive they are to these women. It's not uncommon to find men on death row with a fan base getting lots of mail from women with offers of marriage.

IMO... The religious cases are about people wanting to be part of something "important". (not in all cases obviously)

Often in our modern society people become disjointed and lost. They lack purpose and are generally unhappy.
Converting to Islam and going off to join the fight is very appealing to some of them. Again it's a small percentage of people who affected like this.

With over 7 billion people world wide this phenomenon is really is about numbers.

Think about this...

There are about 1.57 billion Muslims in the world. Lets be conservative and agree .01% are extreme radicals. That equals 157,000.

157,000 is a lot to deal with.