I just can't comprehend how it's considered rude to ask someone to contribute in the party for more than 20% (or less) of the time - especially when the exact same principle is applied to all the jobs: I would ask the same from a tank or DD who'd afk for 80% of the time too. And I do always ask nicely and politely, saying, for example "Hey [healer], since the tank or anyone else isn't taking much damage here, could you please put some DoTs up / use Holy / Gravity?". Just like I'd ask for a BRD to sing Requiem if they're not otherwise doing it.
Then, if the answer is "no, I'm here to only heal", or even worse, "I'm here to /follow the tank and drink coffee while my fairy heals"...
How come it's not considered rude to flat out refuse to contribute as much as the rest of your team, but instead it is considered rude to ask party members to contribute evenly?
Of course I wouldn't support kicking a new healer who's learning their job and the instance and are busy enough with all that without any DPS. But those who're comfortable and familiar with their job and the instance and are simply refusing to be helpful when they could, after being asked to do so in a nice manner, I see no issue kicking.