I think Riker secretly was fine with her destroying the Crystalline Entity. If you look at his expression just as he and Picard are looking toward Dr. Marr, Riker has what appears to be a very slight smile.
And I can't say I blame him.
And it makes up for his being angry for not getting his proverbial potato salad earlier in the story...
He's not wrong in his assertions when he was talking with Picard in the ready room. One of the primary jobs of Starfleet officers is to safeguard the lives of Federation citizens. (A point that Admiral Necheyev made to Picard in "Descent" when she, correctly, took issue with Picard's decision about not trying giving the program to Hugh to infect the Borg.)
^^this
It was one of the highlights of "Descent" pt 1 as well as the dire situation created by Picard... which sadly ended with another "Brothers of Soong" song
I get what Picard was going for and it's a great goal, but where does it end?
Keeping the Crystalline Entity (and every other one out there like it) confined (for lack of better term) but with obtainable comparable electrolyte and salt energy sources they need? Like a sanctuary or preserve. Then again, "The Man Trap" showed a possible outcome on a far smaller scale, the moment the salt went out, but thankfully the entity didn't shapeshift into a hottie to lure you with. (TNG could be so antithetical to TOS at times... yet not quite apocryphal either...)
Of course, how many are out there, how do they travel (and FTL??) but that little problem was common in TOS as well for various baddies of the week and one had to roll with it...
What I mean is that all evidence shows the Crystalline Entity only hits class M worlds with life or that can have life. (It even kills all life on ships, as we saw happen when they answered that distress call.) Eventually, you run out of uninhabited worlds that you can feed it and the only ones left are inhabited ones. So what happens then, just let it kill all the people on those worlds?
YEP!
There's only so many outcomes. At least Picard tried, though the number of steps needed to go from "
tap tap tap, Penny" to "Hi there, can we work together to help you survive without frying every planet that we biological fritters need?" required more than 40 minutes, but the story also wasn't going to end on a note as any given Brady Bunch episode where everything was neatly resolved after 23 minutes.
It's unfortunate, but I think it was the right call to destroy it.
It may be a no-win scenario.
I'm not sure if the makers saw "Datalore" and wanted to "add depth" to it. I can sorta see it, and yet it doesn't fully land. Never mind the sacrificial lamb of Riker's latest hottie for whom he's upset over because she dared to save an old man. It's a character moment that's on par with how Riker was written in, say, "Justice".
One thing that this and "Datalore" never answered: how did Lore even know the Crystalline Entity existed to begin with? And how did he find the time to figure out how to communicate with it so he can betray the colonists to it?
As with FTL travel, the mysteries of the universe are-- wacked, at times. It's oddly easier to handle these big space fritters who somehow end up in deep space despite no hint of FTL ability than it is for the coincidence needed for Lore to have stumbled over it in the first place (and
before he was dismantled and shelved in the largest packaging case ever*, where he was also mooning anyone who found him along with the audience thanks to clever camera angles).
* but designed with cryogenic dry ice fog and what not because even technological components unused slowly start to wear out, even if unpowered and unused. Just nowhere near as fast, but anything to limit or halt the degradation. For example, a real-life computer system (made in 1977) sitting on a shelf for 50+ years without being plugged in will likely still work without issue for a long time if stored properly. After 60~70 years or more, it may eventually develop problems, but MTBF is still an estimation based on known values extrapolated and other unknown variables might still exist (quality of materials, storage conditions, etc - avoid heat and humidity...). Working lifespan** would be less depending on type of chip, substrate, and other materials - any half-life for the whole constructed item is arguably more dependent most on the half-life of the weakest material used in the most integral function of the chip. (if the casing is plastic, it can start to degrade but not impact the chip's usability.)
** Plugged in and used 24/7, lifespan would be maybe 10 years but I'm not a clock, not even a cuckoo clock... well, maybe a metaphorical sparrow as I tend to flit about into open-facing tangents, apologies if I was preaching to the proverbial choir as well...