Some atheists are not willing to discuss this proposition at all, but a large part of the reason for it is because some theists make wild and unfounded claims.
The intelligent design theory has no real reasoning behind it..... if it did then someone by now would have surely introduced it. The starting premise of this hypothesis is that their must be a God, so everything that exists must be a product of that God therefore the existence itself is proof of that God. Surely you can see the problem in that logic.
If, for instance, you were able to show WHY the existence of Earth shows reason for a God then we are all ears...... however circular logic doesn't hold up and is infuriating to rational people. The problem is that this can never be shown..... it can only be stated, which means it is not even at the level of hypothesis no less theory.
So atheists shrug it off as simply a religious view because that is what it is.... until such time as someone (anyone) can throw some legitimate reasoning behind the concept. The universe being vast is not in itself a proof of God..... it is merely a proof that the universe is vast. You cannot make leaps in logic based on unfounded assumption and expect people to take you seriously.