Obviously there is nothing uncouth or innately bad about adverbs.
But I would not consider this terrible advice (although it is dispensed ad nauseam to new writers), because the overuse of adverbs kind of empurples your prose in a way that suggests you’re trying too hard. It can look amateurish; it can be gaudy; it can ruin a reader’s experience by totally demystifying the narrative. I think a lot of the enjoyment derived from reading comes in the form of constructing a narrative and filling in what the author doesn’t tell us. If you decorate every simple action or statement with adverbs, then there is no room for the reader’s imagination. There is no ambiguity, and ambiguity is a necessary aspect of literature.
He looked at her longingly.
“I love you,” he said passionately.
She quickly glanced away. “I can’t be with you,” she said guiltily.
And so on. Ignoring the fact that this is incredibly cheesy, everything here feels exaggerated. Life doesn’t really work like that; actions don’t have clearly designated connotations in reality. Most of the time people just do things. They don’t do things quickly or humorously or vigorously or sincerely or beautifully. They just do.
So when people say using adverbs is “lazy,” they may be right. Adverbs can provide a quick and effortless way of characterizing someone, and inexperienced writers who use them too frequently often fail to characterize or describe in more meaningful ways.
I would, however, warn you against people who say that economy of language necessarily means bare or laconic sentences. Not everyone wants (or needs) to write like Hemingway.