Is it bad to start an introduction with a direct quote?
While I am not aware of any hard and fast rule against it, I would find it off-putting to read a scientific document that started its prose with a direct quote.  There are just so many ways to start with one's own words that it feels lazy and lacking in self-confidence to me to use another's words for the first impression of a reader.

Note, however, that I am speaking of using a quotation as the first piece of one's prose, as distinct from the practice of putting a separated "thematic" quotation at the start of a document of chapter. I see this somewhat more often, and though I find it a bit "cute" in scientific work, I don't have a problem with it the way I would if somebody starts their prose with a quotation.