Why not dismiss the trinitarian belief outright

[arewethereyet]

Theists arguing over their imaginary friends

Your ironic statement is misplaced, sir. No theist except myself wrote any reply in this thread.

There are very compelling arguments for God out there, you know... I am not sure if you are a young fellow trying to please some members in this forum by defending atheism, or a grown atheist. I would suspect it's the former. Here is a sincere advice from me: you won't be finding any truth in internet forums, especially this forum, where argumentum ad nauseam is a widespread tactic, why not take a more neutral stance toward belief and religions and think coldly about this issue before returning to discussion and debates? Religous belief, or the absence thereof, is a very serious matter, you know.. just make sure you got it right.

You will get more insight into the answer to your question from someone who believes in the concept of the trinity.  Most of us left such faith practices which in part means that we don't buy into the concept.  That shouldn't be difficult to understand.  

Why do people believe what they believe?  You have to ask them.

But I will tell you that William Lane Craig isn't the ultimate source for such things as he is pretty fringe.  Find yourself a nice middle of the road Christian to explain why they believe what they believe with regard to the trinity.