It works both ways, you have players expecting to be carried/players who don't know content.
I think it's far better to have an upfront discussion about it, I have had zero issues taking new players through content in the past in any game - we all start somewhere, but it's important to know what you are dealing with/do they have time for a full run/do they have voice comms/will they quit and whine if it doesn't go to plan after 3 wipes....etc... We did a raid on saturday, we were very clear about what our position was (we wanted to go in blind) we had 2 fantastic guys from ocuk with us who knew parts of it and after a few give it a go attempts, they provided an outline - it was a great laugh and I think we all had fun.
This raid is far from an idiot tank and spank, it's quite difficult and requires everyone to contribute (I think it's fantastic) but you NEED to be going in with like minded people and if you are wanting/joining an established team for the raid then you need to take some responsibility and learn some of the basic mechanics.