> Surely the benefit of having these boosted economies doesn't outweigh the negative aspects - or do they?

I think the answer is that with well-managed development, having boosted economies can have few or no negative aspects, but the Bay Area is sorely lacking that right now. As others have said, the lion's share of the blame is not with the tech companies (they're just hiring workers they need), but with the area's terrible NIMBY politics that are blocking the construction of more housing.