It's not a question of whether it's biased to say that, rather whether it would tend to bias the model's response (e.g. toward weighting the stated downsides as more imported than the implicit upsides). But that said, choosing to highlight particular facts while leaving others silent is a very common sign of bias.

Presumably some experts are also optimistic about positive benefits, so we already have bias from only focusing on the negative.

And, in fact, this is true of every single political question you can ask: the 10th dentist is concerned about negative outcomes of brushing your teeth daily. So there's a bias in only saying this in some cases, but not others.