Not sure who you're arguing with, but assume it's an Astros fan making the case that a runner at 2nd base stealing signs is no different than what the Astros did.
That argument is obtuse for many reasons, but the inability to distinguish the differences between the two situations is stunning to me. Your analogy makes sense, but I think there's a more analogous example to use.
Signs are a form of communication. The same as talking. I'm sitting in the VA clinic right now and several different people here are having conversations some of which are fairly quiet suggesting they're trying to avoid others hearing what they're talking about. If they don't want me to hear they could go somewhere else more private, but if I do hear it they can't blame me for eavesdropping. I'm just sitting here in the waiting room. That would be a closer analogy to sign stealing from 2nd base.
Now, let's say I set up electronic surveillance cameras in the wall directly across from them in a private room that could read their lips and translate every word they said for me. Then, after reading the transcript I got sensitive personal information and utilized it to my benefit without them knowing. That's what the Astros did.
That's quite a bit different than overhearing a private conversation in a public place. In the first example they knew there was risk they could be overheard, but they accepted it and tried to disguise their words. In the other example they were oblivious to a risk of being overheard. Consequently, they took no additional precautions to disguise their words.
It just seems painfully obvious how traditional "sign stealing" and the Stros/Sox scandals are different. I'm flummoxed how others can't or refuse to see it.