"AI is just a tool" is meant as a counterpoint to AI producing slop [1]. It isnt that there aren't ethical/societal implications with it as with everything we do in society.
[1] If you take the slop and manually fix/improve/verify it to production value it can be immensely valuable.
This is also how I have seen this particular thought terminating cliche used. The problem with the framing is that on the one side you have someone complaining about unrestrained slop and then this thought terminating cliche is offered. Why yes, it matters how you use it and the complaint is that users are not refining the output enough before presenting it to others.
The thought terminating issue with the phrase is that it isn't just a tool. Once you automate its use (automated PR reviews, ticket fixups, etc.), it becomes a process as well. You are almost certainly purchasing it as a service and not as a tool. It also contains elements of randomness that most tools do not. These quibbling points are what triggers the cognitive dissonance to produce the thought terminating effect. It is quibbling so you cannot really argue that point but the point is irrelevant; the second part of the cliche seems to be agreeing with the complaint about slop and yet the sentence is offered as some counterpoint. This termination prevents the actual conversation about how valuable its use is when the quality standard is not lowered.