I have yet to see any credible "sightings" of UFOs. Most of them are reported by some ignorant hick in Arkansas.
Velocities slightly below the speed of light don't violate any of the known laws of physics. Warp factor 10 does. If intelligent life exists elsewhere in the galaxy, then there should be numerous civilizations that are hundreds of thousands or even millions of years old. That's plenty of time for them to spread throughout the entire galaxy, and evidence of them would be unavoidable. Yet, so far, we see nothing. No radio transmissions. No visits. No nothing.
I think you should do some research, there are reports of sightings by airline pilots, military personnel, law enforcement, and a whole lot of other people that are far from "ignorant hicks from Arkansas". There IS evidence, and while one should not accept reports such as these as fact, even those of some of the most reputable people on the planet, neither should we dismiss them as nonsense either. And our known laws of physics may not necessarily be the end-all, be-all of the laws of physics.
Should we see evidence beyond those reports of intelligent life elsewhere? Seems to me that is a bit arrogant on our part, if a species is advanced enough to get here then it is also possible they are advanced enough to avoid being detected by our relatively unsophisticated equipment. Perhaps our detection devices are still a little bit too primitive.