As someone who is writing adult fantasy and repeatedly discovers that agents who say they take fantasy really seem to mean they take YA fantasy (judging from all their recent query requests, at least, or the details of their MSWLs), no I don't think there are any widely generalized negative views about YA in the publishing industry. It appears to be a very lucrative demographic, so lucrative, in fact, that the last pitmad and SFFpit contests I entered seemed to be dominated by YA tweets.
So it's possible there may be a few people who actually specialize in adult fiction, or who write it, who want to create a space where people who write adult fiction and people who are looking for it can connect. I don't think it's intended as a slur on YA at all. You might as well say that a pitch event that specializes in SFF or MG fiction is casting aspirations on other genres or on mainstream contemporary fiction or on other age demographics besides MG.
Agents and editors specialize in certain kinds of fiction, just like writers do is all.
And those classics you mention aren't actually YA in the modern sense, even if they have children or YA's as protagonists. They were written before YA existed as a separate marketing demographic for one thing, and the novel To Kill a Mockingbird had a protagonist who was younger than a teen (so by age alone, it would probably be MG), but it was narrated by adult Scout looking back on her childhood, not by Scout as a child or teen. So it would likely be classified as adult fiction, even if it were written today.
A teenaged protagonist is necessary, but not sufficient, for a story to be considered YA in today's market. There's a lot more to YA than just the age of the main pov character/protagonist.
I don't think you'll find many people commenting in the YA forum on AW who think YA is just about "cheesy romances," and in fact, if someone said that they'd be taken to task for not respecting their fellow writers (writers of YA and writers of romance).
