Given that the conference is in the future and they could well enact more of these zones, it feels perfectly reasonable to me that some organisers might feel that's not worth the risk.
Your reasoning isn't too different from the above. Gdańsk is a liberally-governed city.
Even if Gdansk is liberally run it sends a signal to legislators that policies effect revenue and gives them a reason to push back that avoids moral arguments. That being said, I think it cedes the moral argument to the opposition, but any fight like this has multiple fronts.
The reasoning is very different from what you wrote. Surely, you see the difference.