Downvotes are an element of the HIVE blockchain. They are used for users to express their dissatisfaction with blog posts. In theory they make sense. Just as there are upvotes, there should be downvotes.
The problem is that we are human beings. We react psychologically to downvotes in a negative way. It is true that some users will try to "use the system", publish illegal material, or publish plagiarized content. The problem is that the ones who take upon themselves to act as police are not necessarily better morally equipped than the accused of publishing "bad content".
These "guardians of the HIVE purity", when they have significant power in the blockchain, abuse their power through the vehicle of downvoting. They do not analyze the content. They hit before asking questions.
Socially, this has the effect of keeping people away from the blockchain. Without the increase in numbers, there will not be a successful blockchain and the financial success will be measured as the total market capitalization and its relative comparison with competing networks.