As a theist you believe in a god. But what about all the other gods? How can you say yours is the only true god when the fellow next to you has his own holy book or ways of worship?
How do you know there is not more than one, are maybe you are worshipping different faces of the same supernatural being who is having a laugh?
If your god is the true one, why does he allow other gods to be worshipped?

Because Jesus speaks to their hearts, silly! :p

You're last question (why does God let other theists worship other gods) seems to be easy for Abrahamic theists to answer: free will.

Yeah, these other gods are just products of man. You won't stump them with this line of reasoning.

Now, other religions do have uses when debunking certain lines of apologetics. For example: when talking to a theist that claims their belief comes from a personal, divine revelation, you can point out that adherents of other religions make the same claim. Their only options are:

• Ignore you
  
• Claim you're/they're lying
  
• Claim their revelations are born out of confusion, but there's are the really real deal (with no explanation how you can tell the difference).
  
• Invoke some "all religions worship the same god" argument (which sort of cheapens the whole thing).
  

My wife is a bit of a fan of the last approach. She said she thought all religions were "correct" in that they all point to the same true god. I told her that she still thinks Christianity is more correct. When she disagreed, I asked her if Jesus is the son of God or if he's just a prophet and not the son of God (like Islam claims). She admitted that she thought Christianity was more correct, but she still feels all religions point to the same god in some way or another.

Careful!, Zeus is getting very angry.
and he has a point too!

He wants to know why the "new age" god is more popular. Has he got more credibility than him! Is it the clothes he wears?
He says that people just worship any bullshit god they get told about these days.

He just can't believe how gullible mankind has become...

Zeus is so yesterday

Same as RobbyPants mentioned and honestly you cannot speak to these people logically their brains do not function properly I am thinking of writing a Doctoral Thesis on the subject.

On the christian forum I am on, I asked for their opinion on the Pope's statement that atheists can now go to heaven as well, no one answered the question or even tried they all posted stupid shit like:

"The question is are YOU going to heaven", or "why did you even join"

So their answer will most likely be a combination of deflection, evasion, redirection, und total lack of answering the question all together.

Why can't religious people just say:
Yes, it doesn't make a lot of sense, I can't prove it scientifically or logically, but I want to believe there is a god.

That's it. ... We're all friends! Let's go make some pink cookies together!

I can't understand how nature can create humans with no reasoning capabilities.
I wouldv'e thought that reasoning is just another survival instinct.

Seriously, is there a possibility that their genome has drifted so far away, that science is at the stage of re-classifying these types of life forms?

I like "homo ignoramus"...... But then, that's just my vanity talking..... Hehe

The fundies will tell you that it's Satan tricking them.

I'd like to see Odin kick their asses.