Making it optional is not a real option. Once you have that kind of crutch, the developer is forced to plan and implement encounters based on the fact that it exists, making the option redundant.
Moreover, if someone in the party uses it, it still influences the whole party, without even mentioning that parties will expect everyone to use it because it makes things easier for everyone.
Such an option simply shouldn't exist. People have tanked without it for ages, with no problems. There's really no need to add such an immense crutch, removing any kind of tension from fights.
Actually tanking with your own skills without following the on screen instructions is too challenging for you?
It's that simple. At the moment FFXIV is not really in any way
challenging. People have
clamored for
challenge, the devs have
promised challenge.
removing the
challenge of hate control by providing easy on-screen instructions is nonsensical.