Well this thread certainly made me sit back and stare/research. Oddly enough FFlogs seems to be broken on my char (And I'm content with that :P ) - My 2 cents is this.
Tanks are supposed to tank. Period.
Healers are supposed to heal. Period.
DPS - need I say more?

If the tanks and healers can dps - great...bonus.

The only time this isn't the case - is if the following is true: Extra Tank on the field (like Raids/or multi Tank situations) - Party doing so well that healers are not needing to heal as much.
Now I can get Extremes/Ultimate having a unique situation where the tank needs to do something different. But in all honesty it depends on the party.
Bottom line - if you get yelled at for some stupid ass log saying abc and is not up to the standards of some random idiot....report them and walk away.
SE doesn't give a crap about what your logs say - what they do care about is you are not hindering the experience. So long as you are doing your job at its basic form - and the party is getting the job done...you should NEVER be kicked for that. What happens in the end is not known - but this much I have found out on my own. Perfectionism is not SE's MO - unless your doing Extreme/Savage/Ultimate that are seriously unforgiving - but that impacts everyone.

honestly I'm against this parser crap - It leads to opinionated elitist morons who judgmentally condemn random players. Yes - I don't deny that it can help greatly for players who need the help - but its akin to being utterly discriminatory. I have a mentor who uses one - and he's ALWAYS constructive. I'd say he's the exception to the rule. Unless you attack him - then he's got ammo lol. (very experienced and knows his stuff)

Thankfully I've not encountered this myself - I will say that being honest about "being a sucky player" up front tends to remove the tension - that way if you get yelled at...they are the idiots...not you.
I see this ALOT.

Not sure if what I said made sense....and honestly people who think otherwise can jump off a virtual cliff cause I play for fun and enjoyment...not for the speedrun addicts. (Pull more! (healer says this and promptly dies afterwards....yep..been there done that))