The official stance makes sense if you understand Square can't dictate the applications you install on your computer. They could in theory put a rootkit on that detects ACT, but those are always found out and disabled. (Think nProtect GameGuard and PSO2).

ACT is a packet sniffer that will decode specific packets, analyze them, and display the result. I could run a tool like Wireshark and it has the same underlying effect. Plus if I were a more ambitious engineer, I could write a similar program. All the modding programs simply change the DAT files. At the end of the day, it's my computer and what I run on it is my choice.

What Square is ultimately concerned about are third-party applications that modify the information being sent to the servers. Speed hacks, item dupes, etc. The thing is, it's far too expensive on their end to analyze all the various tools out there, so they issue the blanket statement of "No third party applications." Additionally, they care more about how the third-party application impacts the online experience. Obviously speed hacks, automation tools, and item dupes are just cheating, plain and simple. With ACT, as many have said, it's not about using it, it's about using it to harass other players. Even if you say you use ACT, I doubt Square will do much because they can't really prove it's anything other than a claim. Maybe a warning, maybe a temporary ban. At the end of the day, so long as you don't harass other players and don't cheat, it's not worth the effort to go after you.