You determine whether something is a net positive or net negative by listing all of the negatives and positives and seeing how they balance out. With the internet, there are clearly both negatives and positives. The "evidence" either way is the full list of these factors.

Do they balance out in the positive or negative direction? The answer to that depends on how you weight the various factors, and I rather suspect that different people will weight the various factors differently. In other words, this is more a judgement call than some sort of hard objective truth regardless of whether you consider the net effect to be good or bad.