Kevin threatens the away team with a phaser, but Worf easily spots that the phaser is nonfunctional and does not heed the threat. We later learn that Kevin has created everything in his home using his abilities, which means he specifically created the phaser to be nonfunctional. The pacifist Kevin won't even create a working weapon for the purpose of a bluff.
Kevin put aside his powers to act as the mortal husband to Rishan for decades. He might have been able to fool the Husnock and/or Enterprise if he wasn't so out of practice using his powers or even thinking in those terms. This might also explain the spell he put on Deanna having a far more devastating impact than he likely intended.
Kevin was also living with his sorrow and guilt. Deanna being able to sense what he really is (and that his wife was an illusion) angered him and instead of a fine-tuned effect, he lashed out with his power. He pretty much admitted that to Picard when he explained himself.
Fridge Horror: How powerful, exactly, are the Douwd? We never even hear the Q Continuum acknowledge them. Maybe it's for the best we only hear of them in this episode. They are certainly one of the most powerful races shown in Trek but are most likely still far below the godlike Q in power, particularly as the Douwd apparently have no ability to manipulate events outside of time the way the Q can, as Kevin could not reverse his genocide after committing it.
Kevin is presumably not omniscient, as Picard was able to hide the Enterprise from him and blindside by abducting him from the surface against his will. How, then, could he have known that the Husnock were an Always Chaotic Evil race? Only one ship attacked the colony, and politics is complicated; they could have been representing only one faction out of hundreds, they could have simply been a band of pirates operating on their own rules. For all we have been told, the majority of Husnock could have been peaceful, and if this were the case, Kevin wiped out an entire innocent species based on the actions of a few rogues.
It’s possible he was lying to assuage his guilt, but he’s also immortal and may have visited them before.
An Extended Universe novel shows us the Husnock at the moment of their annihilation. They are indeed as unpleasant as Kevin suggests, but their end is still portrayed as horrifying. (And the abrupt abandonment and therefore availability of their lethal technologies turns out to be a whole other existential threat.)
Pretty chilling to think, as awful as Kevin's extermination of the Husnock was, it may have been the only thing that saved the Federation. After all, this entirely unknown, heavily armed, warlike state was making its first incursion against the Federation. We don't necessarily know how they would have fared against a colony with stronger defences, or against Starfleet vessels or bases, but it could well have been devastating. And worse yet, we're less than a year away from the Borg assault. Starfleet, to which a single Borg cube handed its ass at Wolf 359, might well have had to go into that battle while fighting a war against the Husnock at the same time, if this random colony hadn't happened to have a Douwd living on it.
Presumably, there are other members of the Douwd species out there, living among us (or perhaps among Vulcans, Klingons, etc). And all we can hope for is that no one upsets another, maybe less pacifistic, Douwd.
Kevin said that Douwd are beings of "false appearances". It's likely that any others of his species assume the appearance of other races and "die" when things get complicated. He also implied that he wasn't from this galaxy.
It's also possible that it was only Kevin's extreme rage and grief that caused his powers to go into overdrive to the extent that they did; after the extermination is over, his powers are shown to be fairly limited, to the point where he has a hard time shooing the Enterprise away, when he could have just teleported them to the other side of the quadrant, or made Rana IV vanish completely. So even if a Douwd had sinister intentions, they probably couldn't wipe out a whole race on a whim under normal circumstances. In this case, we just have to hope one of them doesn't get triggered the same way Kevin did...
The fact that even though they may very well have a law to deal with the scope of the crime Kevin has committed (genocide), the Enterprise is completely powerless to do anything to enforce it and all they can do is leave the planet and let Starfleet and its allies know what happened and to steer clear of Rana IV and hope that Kevin doesn’t lose the one thing keeping him in check, his own morality.
People sometimes wonder what Picard meant by "We have no law to fit your crime" — surely the Federation has laws against murder, let alone genocide. But he may well have meant not "we have no statute to fit your crime," but "we have no legal system that could fit your crime" — no practical way to impose judgment on Kevin unless Kevin freely chose to cooperate with it, which he's already doing with his own self-inflicted punishment. In other words, the law isn't ignorant of his crime, but useless before it.
In real life many actions can somehow be gotten away with because the people who made the laws never imagined that someone would be evil, ignorant or stupid enough to ever do it. The Federation likely does have laws against genocide, but genocide as a crime of passion? I doubt they ever believed such a thing to be possible - even if Kevin did cooperate and stand trial, how do you factor what would normally be a mitigating circumstance into a mass murder charge?
