I can strongly disagree or disapprove of a position or person without bringing hate into it. eg. back when I was pseudo-religious and kept kosher, I was fine with seeing and smelling pork products and listening to my friends go on about how tasty pork products are, because I was completely confident in my choice not to eat them. No emotional bolstering required. In the case of Scientology et al. it's even easier to be confident, because I would have to undergo brain damage or some kind of severe personality modification before their beliefs would look plausible.

Also on a more pragmatic note, humans aren't good at separating people from their opinions. If you cultivate a hatred of Scientology and then meet someone who used to be a Scientologist but left, there's a very real chance that I would feel dislike for them purely based on their past affiliation, and that's not a behaviour I want to endorse.

As a rule I don't think hatred is very often a useful emotion to cultivate. Even if I decide before hand that a position is so bad that it deserves hatred, calculating calmly and rationally, after I have hatred towards a group it clouds any rational evaluation of them. It's possible I was missing important evidence when I first came to that conclusion, but having hatred makes me less likely to re-examine the evidence and decide they're not hate worthy. Maybe they change how they act subsequently, once again I will struggle to re-evaluate my position.

Further, even if I knew for sure that neither of the above situations could happen, hatred is generally not a useful emotion because it:

• Clouds insights on myself I could gain from these groups. Perhaps particular decisions or beliefs they made or acquired led to their current status. I could learn a valuable lesson of what to avoid from that, but hatred makes it more likely that I will view them as other to me, and not want to acknowledge that I could make similar mistakes, and so should be wary of them.
• Is generally not very pleasant. Hating people can increase stress, especially if I come into contact with them or mention of them often.
• Diminishes the power of any warnings you may try to deliver to people regarding them. Trying to dissuade someone from joining them, or trying to warn people about some heinous action the hated group is undertaking is a lot harder if people are going to dismiss you because of your hatred.