I'm not basing that statement off an assumption. I'm basing it off of evaluation and observation of the fish. There is a reason this stuff kills the worms, snails, and crustaceans in a tank. Ultimately, any medication is a poison.
Now that is true, and I don't deny that uninfected fish sometimes seem a bit subdued. Or that the necessary dose is about half the fish LC50 I saw in one research paper. This worried me enough that my first treatment attempt was half what Charles recommended. It didn't work.
Though I haven't seen any snail deaths, or recall seeing anyone else report this. Did this happen for you? If not, are you possibly confusing Levamisole with Flubendazole, which is a guaranteed snail killer?
This worries me as my research into the topic showed that this is happening more and more among keepers. levamisole appears to be the only viable option of treatment
It worries me too. A lot. Callamanus is only becoming such an issue now because it's developed resistance to most common anthelmintics. If it develops improved resistance to Levamisole too, we're in trouble.