Is that a reasonable assumption to make? I don't think we have any evidence of other places we look being "largely the same" with respect to life conduciveness. It took billions of years for our own planet to achieve multicellular life, which is a significant fraction of our best estimate of the lifetime of the entire universe up to this point.
But the universe is big and there are billions of billions of other planets which could very well have similar conditions, that also exist for billions of years
The question isn't about what's easier to believe, it's about what the evidence supports. The probability for life (or multicellular life or intelligent life or technological life) to evolve on any given planet is strictly between 0 and 1. You can believe what you want, but the facts don't support any stronger statement than that.
