True, and even if a smoke grenade was effective, there are a lot targets for which that wouldn't be practical. Would an incoming cruise missile need to deploy a string of smoke grenades ahead of itself?
I'd be more concerned about the smoke/fog being sufficent to interfere with optical tracking of the target. I'm not sure that radar tracking is sufficiently accurate for laser targeting.
The 'additional effect,' IMO, is that there is no single naval weapon that works against every threat and is immune to countermeasures, so we shouldn't hold the laser to that standard. Deck guns are useless against submerged subs, torpedoes are ineffective against aircraft, cruise missiles are ineffective against TBMs, etc.
So, sure, there are targets for which the laser will be ineffective, and sure there are countermeasures or environmental effects that will reduce its effectiveness. But will the laser be effective often enough to justify the cost, or would the ship be more effective if it had, for example, another CIWS* mounted instead of the laser?
I don't know. I strongly suspect that the USN doesn't know, either, and that there are intelligent people on both sides arguing that this will or won't be very useful. If that's the case, then it certainly seems reasonable to do a limited deployment of the thing and see how it works out.
*FWIW, I have no idea whether the laser system takes comparable space, weight, etc, to a CIWS installation.