I am of the opinion that people generally don't change. But the urge to conform to the group is a powerful urge, and public ridicule is one of the few methods that has a possibility of changing someone. Not the most popular view I know. So pile some ridicule on and maybe I'll abandon this view point!

The confrontation of this street preacher is a bit more explicit: https://www.youtube.com/watch?v=iIdvRPq37FU

The mocking section only extends to 2:50. A guy In a dog suit found a imaginative way to mock a street preacher. Opinions may vary on the effectiveness of the humor.

Why should we mock people that believe stupid and immoral things?

hmm.... hard question. :)

Imagine what would happen if people believed false things(we don't need it to be immoral).

Imagine that most people do not believe in empty plane fuel tanks.

After some plane crashes those believers will come with an apologetic that it was not the fault of the empty fuel tanks, but something else.
Do we need to mock these people to make them see reason?
The answer is obvious.

So after we see religion be used as a mind control tool, by people in power to commit:
Crusades
Suicide bombers
Ethnic cleansing
Inquisition
Systematic fucking of children
Burning witches
etc...... trust me the list goes on....

After some time those same believers will come with apologetics that it was not the fault of Religion, but something else.
Do we need to mock those people to make them see reason?
The answer is obvious.

Religion is the VERY FIRST weapon of mass destruction; Mind Control.

Religion is the only mind control weapon humans haven't banned yet, simply because too many people are infected by it.
Mockery is a possible way to heal those infected people.

Mocking the ridiculous and intolerable is often the only useful fulcrum of change.

I like the way the maker of this video mocks some christian scammers, funny: https://www.youtube.com/watch?v=ab0HCYjzSro

Kean, I don't know that we 'should' do anything. Rather, we 'could'; mockery is one of a multitude of options. I find mockery to be a harmful behavior, and of little use to creating meaningful dialogue.

But then, meaningful dialogue isn't always the goal. Sometimes, self-soothing is the goal. Enter mockery, and other forms of ad-hominem attacks.

Used sparingly and wisely to point out absurdities and contradictions, mocking can be quite powerful. I can't deny that such played a role in my de-conversion. However, continuous, cruel and hateful mockery that ridicules sincere and well meaning people is something I consider ugly. It also encourages some believers to stand even more strongly in their faith and feel more justified.

What is wrong with mocking religion? People mock atheism. The difference is that theists get angered when we mock their baseless beliefs (I say baseless because the bible is no proof of anything other than indoctrination was possible back then), but I don't get angry when people mock me on my disbelief. What is there to mock? "Haha you don't believe in God!"
"...Ok?"

I knew someone would like it. Yours makes me laugh, it's something I want to hang on my door

It's been years since I watched the show, but I used to like the restrained mocking in The Simpsons. It showed church goers as a mixed bag between the sincere and devout and those who just felt they were supposed to go or who went out of habit. The pastor was burned out and cynical and as irritated by the zealous (Ned Flanders) as he was by those who slept through his sermons (Homer). I also liked the little jabs, like the one I remember when the Reverend asks God for a miracle, looks up into the sky, pauses, then sighs and says "fine, we'll just do it ourselves...again". Little mocking jabs like that actually had an impact on me when I was a believer. Huge scale attacks on Christianity however with the clear intent to offend, just made me turn the TV off.