What very few critics of Scientology (or any other betterment activity) realize is that they are undermining another’s purpose.
When a person enters Scientology or any of the thousands of self-betterment activities in the world, that person has an underlying purpose for some kind of improvement. It can be anything from handling a problem to improving a situation. This purpose can be so strong as to blind him from any negative effects of the path or method he now trusts.
And then a critic enters.
Whenever you criticizes another’s beliefs, you attack this underlying purpose of improvement. You corrode his trust in something good. The method may be mad according to you, but his underlying purpose of improvement is almost always good. You may not realize this, but this is usually why the believer reacts so violently to your criticism – often with stupid justifications or “logic”.
The solution should always be to present a better method for the person to realize his underlying purpose. But alas, this is so much harder and requires so much more responsibility on your part. It is far easier to slash away with harsh criticism than to help the other find a better way.