You said "a great way", which while perhaps not the best way, surely must be pretty close.
I think a great deal about what you say. I understand the arguments you make, but I think you are giving too much credence to what are essentially random theories. The problem is that you seem to be interpreting "possible, with indeterminate probability" as 50/50. As if for any event for which we do not know the probability of, we must treat it as equally likely as the absence of that event.
I think this is very interesting issue, and one that leads to a great failure of communication between skeptics, and non-skeptics.
It's also one that's linguistically easy to convolute the logic. If there's no evidence for something, and no evidence for the absence of something, then it's easy to "reason" that that means there's a 50/50 chance of that thing existing (or as you put it, an unknown probability).
I like to try to force people to say how likely they think something is. Because even though you can argue the probability is indeterminate, one still has to conduct one's life. Now if I though there was a 50/50 chance of aliens making crop circles, I would conduct my life in a different way - so clearly I think it's less - far less in fact, a very small possibility.
There's a difference between "indeterminate, yet likely", and "indeterminate, but very unlikely".