Saying that there is either life (let's call it choice A) or that we are special and influenced by an external force (choice B) if I'm reading what you're saying, is just a bit silly.
You have a decent idea, although scale up the size hundreds of billions of times, but you're missing one of the most important parts about the laws of probability. If there is a 99.999...% chance that something exists then there is also a chance that it doesn't exist. A choice c, if you will.
It's splitting hairs to a degree but it is a concept that is very important to remember when dealing with orders of magnitude on the level we are. There can, as amazingly unlikely as it is, be a situation where life is entirely possible in the universe AND we are the only example of it. I do not think that this is true, however, it is a case that must be considered when looking at the situation as a whole.
The probability of life is based on a few things, but the most important of them can be summed up fairly succinctly to give an accurate idea of what we're looking at and what we look for:
1) Ingredients - Hydrogen and Carbon at the very least. These exist throughout the universe so this condition is fulfilled.
2) Planet size - Too small and the planet will fail to support life or an atmosphere in some cases where a planet too large will be gaseous. There are limits to the size a solid planet can be.
3) Location, location, location - Earth and Mars are two planets that fall under what is so aptly named the "Goldilocks" area/region/zone whatever. This means literally what you think it means, not too hot, not too cold, it's juuuuuust right. Now this zone varies in different planetary systems based on many variables, the most important of which is the size and type of the star in the system. If a planet falls too closely to the star it will have a temperature far too hot to sustain life and be bombarded with cosmic rays further prohibiting the creation of life. Too far from the sun and temperatures will be too low for there to be liquid water, which is one of the things we look for in planets that may be able to sustain life.
Liquid water IS a rare thing in the universe. Do not be fooled by the abundance on Earth.
So, tl;dr: The probability of life is directly proportional to the probability of planets in a system to fall within the necessary designation. The overall probability is just a sum of all the probabilities that all (not all are listed here) the necessary requirements for life are met then coupled with the probability that single-cell organisms will develop before the planet in question is destroyed by any number of factors (3.5 billion years for multi-cellular life on Earth in a system that has a sun with the total life of ~9 billion years. Should single cell organisms emerge on a planet on the aging side of a star it may not have the necessary time for life to form.)
All in all it is incalculable, but it is also important to remember just how many variables are in the problem and it is equally important to remember that as long as a probability less than 100% exists there exists a probability for the opposite.