Pretty much this.
If somebody told you where certain thing is, even if it's a bit vague, but he tells you by name, there should be a a quest marker for that.
Remember though, he said there should be a marker for the 'area', not on the object itself, and 'area' is very debatable and vague.
And also, why 'should' there be a quest marker for that? Very few things should, or shouldn't be a certain way. Who are you to decide?
When the quest is about, "finding this" or "searching for that" quest markers could ruin things,
Only
could ruin things? Really? Do you still not get it? The task of finding something for the sake of fun/a challenge, is by complete necessity ruined by an arrow that points to it.
Imagine how fast a game of hide 'n' seek would lose it's appeal if everyone hid and then told you where they were. Don't you think "could" ruin it, is a bit of an understatement pal?
otherwise they're helpful.
This has been specifically addressed, nobody is saying quest markers aren't 'helpful', they're about as helpful as the game doing the quests for you itself would be helpful. The point is many people believe, including me, that they're
too helpful.