It's Ignorant comments like yours that enable companies like SE to continue doing what they do, because they believe it's "Ok".
First off, you should NOT be queuing up for something if you did not have the 30mins-1hr to dedicate to the task. This has been an issue since 2.1 with the release of CT's 24 man dungeon, how could it be overlooked now when you're involving 72 people!
Moreover, you say we are telling SE, "players should be allowed to cancel their queues." so I ask you, why did you queue up in the first place? there could only be 2 possibly reasons... 1.You wanted to do Frontlines 2.You want to be a "troll" and waste others peoples time.(which is now a common thing these days.) I have no doubts people are jumping in, and out of queues just to see the numbers go to 70/72 and hit cancel to give themselves some sort of laugh.
Now complaining will only get us so far. Suggestions are our best bet to getting this resolved ASAP. (because if you actually queued for frontlines you would understand this is clearly an issue) As I spent over an hour in queue waiting to join frontlines, only to see it stop at 69/72 70% of the time.
My suggestion would be "Queue locks" like all other games there should be a MINIMUM entry value. If 24+ people are queued up, and have locked in their queue, they should be entered into the arena.(more can join, during the "waiting period" to reach the cap.) This will also encourage players that WANT to actually do frontlines to queue without worries. Now if those "trolls" or people whose houses are burning down, and have to leave their computer for more than... lets say 2mins?(Like in arena) Should be removed like Normal, and given the 30 min lockout.(This will then help deter trolls, and well people that don't actually have the time to participate.) I know there is still the issue of people taping their controller or keyboard to move forward, to reset the timer. But thats where they have the "Have to engage" or you get removed in 30secs etc. Or the old WoW "Report afk" (which I hated, but helped.)
It's safe to assume there will be some upset people with legit reasons for afking, but again back to my first point "You should not be queuing up for something if you don't have the time to dedicate to whatever it is you're doing" And if you actually had a legit reason for walking away from your computer for more than 2 mins, then the lockout should not affect you, as it should take more than 30mins to do whatever it is you had to do. ie. House burning down prob take a bit more than 30mins, and a game should be the least of your worries.
I've also seen suggestions of removing the queue counter, so not to enable those trolls as much... But thats a small temp fix? that could possibly help.