Hi

what's the difference between saying "just as harmful" and saying "as harmful" or, generally, between "as adj. as ..." and "just as adj. as ...".

thanks for the answer

Marco

When you say "as harmful" you are giving a straightforward assessment. When you say "just as harmful" you are emphasizing that the similarity is surprising in some way. I didn't look at the lesson, but most likely the listener believes that the thing isn't as harmful and the speaker is trying to change the listener's opinion.

Many words are added to either (1) give the listener some hint of what the speaker feels about something or (2) give the listener a hint about how the speaker wants the listener to feel about something.