My feelings and beliefs aside, it's simple statistics.
We know at least one set of conditions that can harbor life. And we know it has happened at least once; we're here, aren't we? So it's already statistically impossible for no life to have formed, otherwise we wouldn't be here to figure that out.
So. Barring some off-the-wall bizarre alien life forms based entirely on the element Aluminum (or any other humorous random non-synthetic element), we know that it is entirely possible for life to happen.
There has to be "aliens" out there somewhere. Sentient? Maybe. We are, right? Advanced? Depends on how you define advanced, but yes, possibly. All depends on when they seeded.
All that's needed is the right conditions. We know it happened once... the question is how common is it? I'm betting it's maybe a few hundred examples in a galaxy the size of ours, less in smaller ones. And I'd wager at least one is "advanced". Though why they'd have any interest in a backwater place like Earth, aside from, y'know, another sentient life form, I couldn't tell you.