Rewarding comments would catalyze the interactivity and boost the whole platform. But still one would replicate the same problem, when it comes to payment people say what they think, that you want to hear. Like prostitutes or those girls marrying 90 year old men. Its their job to say nice things and this is defined by the wallet. The valuable thing of YouTube for example is, that there are true unfiltered opinions, this is why politicians want to censor it. Here people have to fear repression. Downvotes (for personal reasons) made the number of steem users even go down further, whats left are people who are much older than on YouTube/Twitter/Reddit/ and those who are compliant.