I agree that a lack of team attitude can indeed be a hindrance, but a groups back does entirely rest on the healer. You can do almost any dungeon content (with a few exceptions) missing a dps or even a tank while a healer if that is missing you arent going much of anywhere. It can be a lot of pressure. In a group where I can trust the members (or at least the tank) I dont mind tossing some DPS (or in the case of if i am going with my raids tank mostly dpsing) in dungeons trials and even raids (because gravity is the best looking spell in the game and if you havent looked at its animation closely please do the detail is amazing) but in a group of randoms there is a huge trust issue. I am in a group of people who I have never played with I dont know if you can dodge or not and taking early dodgable damage gives me zero faith you will dodge when it comes to boss mobs. Tanks cant stun the AoE of the dolls in "the vault" after pulling the entire hall without cooldowns and body agroing everything so the second I cast any heal I die? Well I am not going to be dpsing much. Maybe its me being bitter after dealing with so many random people over the last 3 years who think their dps is the be all end all that pushes me away from the dps mentality (I actively refuse to play any dps jobs in a group setting even though I have them leveled) of that is all that matters is that number you are doing or tanks who think they set the pace without taking into account that the healer may be a bit undergeared than they are used to or they dont pop the cooldowns I am used to. Tank grabs too much? Healers fault that the group died. DPS standing in too much AoE and die, healers fault. It is a lot of pressure because the second any party member dies its the healers fault and I have on a few occasions had tanks in again the vault stand on the 2nd bosses black orbs take massive damage get the debuffs then whine when they die because of how bad the healing was.
There are bad apples in all roles and I hate healers who even in the low dungeons with faery up then afk on follow (please just kick them for offline afk or even harassment) but healing is a stressful job. I have done all roles both in a raid setting and in a more casual dungeon setting and I can say that healing is by far the hardest to play as its not 1-2-3 (dps) and its not AoE AoE AoE go into 1-2-3 (tank). Every single mistake the group makes the healer has to pick up and a healing mistake while stance dancing or not is a wipe. Clerics stance activates the cooldown on it and you are locked into it for 6 seconds which means no healing for 8 seconds after putting it up. That may seem like a small time but when your tank just took a large hit that should have been avoided and you are stuck sitting there for another 4 seconds watching them at 1k HP praying they mitigate the next auto attack it feels like an eternity. If a healer is not comfortable doing it then dont make them. Accept that it is a bonus and seperates a good healer (party is taken care of and people dont die even if they mess up a bit unless it wasnt preventable (stood in the beam/ran during a stack mechanic/stays in the quicksand/doesnt do instant death machanic right) and a great or amazing healer (you shaved 3-4mins off the 25min dungeon while doing it)
I do not advocate the my sub my rules because there are some basis for community standards but at the same time making someone feel uncomfortable playing this game because they are not at your level of skill is pretty selfish and quite a jerk move on your part.