Naturally I haven't read all 500+ replies. However, the beginning and the tail of this thread do not differ greatly.
Evidence for life elsewhere is not mounting. We don't even have evidence for how life began here. We have many assumptions, wild guesses and informed speculation but we have no idea what the initial conditions were here on Earth that led to the chance occurrence of a self organizing and self replicating organism. Without even that basic knowledge we don't know what to look for elsewhere. We can be reasonably certain that the early atmosphere on Earth wasn't anything like it is today. Free oxygen doesn't hang around for very long without life to replenish it.
The life forms that exist here today are those that have adapted to current conditions. There is also a very large element of pure luck that allowed some types to survive purely by chance when great extinction events occurred. A life form cannot evolve to survive an extinction event nor can it adapt in just a few generations or even a few thousand to survive conditions that are deadly. We do have evidence that a majority of the life forms that existed previously on Earth have failed to survive. The remains of the creatures that are found in the Burgess Shales represent forms of life that were utterly wiped out. They have no present day descendants, nothing that can in any way be reasonably connected to the forms that existed before the event that finished them.
We are lucky that we live in a quiet corner of the galaxy. Of course if we didn't we wouldn't be be here. What is becoming apparent is that galaxies are high energy neighbourhoods and that isn't good news for self organizing, complex anythings. Energetic events have a strong ability to tear things apart. Huge swaths of any galaxy are off limits to anything that depends on persistent structure and organization. High energy environments are inimical to what we consider to be life. Even life that we might not recognize is not exempt from the intensely disordering effects of high energy processes. Wide spectrum high level electromagnetic radiation will disrupt even basic organic molecules as well as inorganic molecules.
This is something for which we are rapidly developing evidence. A black holes forms at the centre of every galaxy and infalling matter spews intense radiation like a Flash Gordon death ray. There is no chance for life to develop, let alone survive, anywhere near the central regions of a galaxy. The Drake Equation needs a few more terms to accurately describe what we now know about our universe. Those terms are essentially negative constants that reduce the probability of life surviving long enough to be noticed. The terms need to include the chances of various extinction events occurring to any particular planet that might give rise to a life form. Everything from simple asteroid impacts to hyper novas in the neighbourhood represent terminal events. Put even weak wild guesses into the equation and what comes out can easily be a negative chance of life developing in any particular galaxy, never mind lasting long enough to develop to a sentient level.
On top of all that we have no idea what it takes for life to go from a self replicating organic soup to something that is able to contemplate that process.