virtually undetected, would preemptively obliterate earth’s inhabitants as a threat to cosmic harmony.

they would have to be outside of this solar system. That means they would have to have longer lifespans than us or their spacecraft would have to be much faster than ours. Even a planet in the Proxima Centauri system is over 4 years travel from Earth at the speed of light which is 186,000 miles per SECOND. There is no Earth-made object which travels through space at 186,000 miles per hour, which is only 1/3600 the speed of light. At this rate of speed, a spacecraft from the Proxima Centauri system would take 14,400 years to reach Earth.
The incredible distances between stars would seem to negate interstellar travel, at least for us. That being said, I have no doubt that there is intelligent life out there but we will likely never know what they are like.

Seriously.

what do you suspect would be the explanation if it is bad?

Like the late 1960s, and now!

on Times Square.

of course there already is a creature there....

Show me some actual EVIDENCE of "alien ships," damn it!
Obviously, they can't or won't.

Just too much money to be made from the flying saucer groupies.

thousands, maybe millions of years ahead of us in technology.

Lots of things most people don't think about when assuming those vague blobs of light are alien spacecraft. First off, the possibility of actual FTL (faster than light) travel is vanishingly small. Which means, as has already been pointed out, even at 99% C(the speed of light), it would take at least four years to get to the nearest star. Even if you assume an intelligent species out there with a much longer life span, that's a barrier to travel. Our medium-sized galaxy is about 100,000 light years in diameter, so actually exploring any significant portion of the galaxy is probably out of the question.

Something else about FTL that My Son The Astronomer told me recently: The faster you go, the more cosmic radiation you'd be exposed to, because you'd be travelling through it so quickly. Which means building a ship with sufficient shielding to protect those inside, might not be possible, no matter how advanced your technology.

Other things: How long it takes for life to evolve on a planet, then how long for intelligent life, then how long for a technological civilization, is a huge unknown. All we know is how long it took these things to happen on our little planet. My Son The Astronomer tells me that a lot of people in his field think we may very well be the first such in our galaxy. Maybe not.

He's in a PhD program in astronomy and is doing research on radial velocity, which is one of the methods used to find exoplanets, planets outside our solar system but inside the galaxy. So far thousands have been found, mostly gas giants, but some smaller, rocky, potentially earth-like planets. Here's a link he sent me yesterday about trying to find extra-terrestrial civilizations by looking for artificial light on the night side of a rocky planet: https://arxiv.org/abs/2105.09990 We are still a long way from being able to do so, and you'll see that what's proposed involves finding planets far more urbanized than ours is.

even intelligent, technological extraterrestrial life, is quite separate from whether aliens have visited us and kept their presence secret.