There is nowhere that we are aware of that could support life right now, except Earth. This is because life requires a great deal of liquid water, a source of heat/energy, and the right composition of elements to allow the creation of aminoacids. Though there might be a lot of "potential" places for these things, the combination required is likely to be extremely rare. Water does not imply life - by that definition, the entire Universe would be a very hospitable place (ice is a very common chemical). There is still the matter of whether "sentient life" will exist in our race's lifespan.
Gliese 581, Mars, possibly several of Alpha Centauri's planets and a bunch of others that I don't have the time to look for at the moment are all candidates for planets suspected of harboring basic life forms. You're right in the sense that we don't have a space velociraptor in a cage, but we have a tidy list of planets we're keeping an eye on because they meet the criteria for now. Water usually does imply life. We're not talking about vegetation and animals, but life nonetheless. That's why finding water on Mars was such a big deal. That said, we prefer to search for suitable star systems first, and if the technology is there, attempt to find the planets therein.
We're alive right now, yes, this much is true - but we have only been the dominant species for what, a few thousand years. It seems remarkably arrogant to presume that we will continue this trend for millions of years to come (a lot of species have already survived this long). Sentient life brings with it the problem that it can destroy itself. If viruses and bacteria progress as they have, it's not a stretch to assume a great deal of our population will be eradicated within the next few hundred years due to population density. There is no way to genetically engineer away viruses or bacteria in a way that will have no serious side-effects, either.
Why are millions of years required to become a spacefaring race? We went from not having airplanes to going to the moon in a century. Unless we become technologically stagnant, which won't be happening in the foreseeable future, we're well on our way to getting "out there".
"Sentient life brings with it the problem that it can destroy itself." is an arrogant statement as you're attributing human characteristics to all life, everywhere. Why are we automatically assuming every race that has a degree of intelligence is warlike and self-destructive? As for the future of humanity, at what point do we become more (or less) than human and begin integrating technology into the human body? Will we be affected by virii the same way if our technology is constantly fighting them alongside our natural immune systems? Do such things even matter at that point?
Evolution dictates that an aggressive tactic is frequently very successful. Take ants, for instance, which have a highly aggressive attitude towards basically everything. There's also the question of whether you could actually have a civilization at all with an insect hive, as there would be no reason to improve it. Intelligence does not pay off for drones (which is what, 99% of the hive).
If there were no room for improvement, ants would have stopped evolving ages ago. Clearly, they have not. With out current conditions, there is no reason for them to be anything more than what they currently are or will become as a matter of course, as you stated. But what if this were not the case on a planet that is not ours in an environment that is completely different from ours? All variables change to such a high degree, that there's no point in even guessing what is and isn't possible because we haven't had any experience with any of the things we're talking about.
There is no reason to assume that alien species would evolve on a planet dissimilar to ours. In fact, that is counter-intuitive. Until we actually discover some form of alien life, there is no way to substantiate your claim - whereas the claim that it would be similar is supported by our own existence, and the existence of all the other life on our planet.
Which is precisely why we're searching for life as we know it. However, it's unreasonable to assume, based on our extremely limited knowledge of the Universe, that the conditions that led to life on Earth is all there is. I'm not sure why you'd consider it counter-intuitive, considering how diverse our planet is, let alone the entire Universe. In fact, the latter is precisely why most scientists assume if we were to encounter intelligent life, we may not even view it as such initially because of how different it would be to us. Most people scoff at the notion that an alien race would have remarkably similar physical features to us for this reason.
I've got to agree with your aggressive stance towards potential aliens, however. We can barely get along with our own kind; how will we deal with baby-eating tentacle crabs?
My stance isn't aggressive. It's entirely defensive. There's no reason to seek our destruction from a race of beings capable of traveling across a galaxy until we know we can defend ourselves from them should they be less than polite. So we turtle. We turtle until we no longer have that option.
