Both of your reasoning is depending on the idea that Ukraine has some kind of decisive local advantage which the Russians would be desperate enough to want to harm their own infrastructure and defenses to mitigate. Outside of the most optimistic pro-Ukrainian propaganda, it doesn't seem very plausible.
They don't depend on that at all: there doesn't need to be an actual local advantage, there just needs to be the possibility of one. Ukraine, by reports, has 50-60,000 newly equipped and trained troops behind the lines ready to throw into action. Some of them could have appeared at the dam and launched an attack in fairly short order.
Once a force has blown up a bridge, they have much less defending to do. Firstly, it obstructs an offensive because it's very hard to cross the river, and secondly it makes operations on the other side of the bridge (even if they do get across) extremely difficult because it becomes much harder to supply the forces, with further risk of being cut off and destroyed by counterattack as their retreat is compromised. As Russia has moved to a defensive stance, it gives Russia every motivation in the world to reduce potential lines of attack into its occupied territory and reduce risks.
The second argument is that Russia would be unwilling to damage infrastructure - really, to harm its own people. This is completely inconsistent with Russia's actual behaviour over the years. Or the Soviet Union's. Or Tsarist Russia before it. It's even in Russia's own rhetoric, Putin and others, about the hardiness of their people and willingness to go through suffering to win, the example of scorched earth in their "Great Patriotic War" to deny the invading Germans. The Russian / Soviet (because Putin is nothing if not a Cold War dinosaur) elites' view of their people as expendable peasants has never really gone away.
Also, the people who will be suffering the most, who already have suffered the most, are Ukrainians. Sure, Crimean agriculture will be short on water for a few more years, but it's already collapsed anyway after Ukraine blocked the flow. Russia has made it absolutely plain that the lives of Ukrainians mean vastly less to them, as evidenced by the smashing of civilian infrastructure, rampant looting, torture and murder within occupied territories.
Just because you want to equate two things doesn't make them equal, nor you more principled for having equated them. Even with lots of repetition.
Physician, heal thyself.