The problem isn't the downvotes themselves. Downvotes are an integral part of SE.
The problem is the low levels of constructive feedback, which is essential for a young site to set and then maintain the high standards of quality which will attract good users.
I've been involved in several SE sites as they went through the public beta phase. The high standards users of established SE sites rightfully expect don't happen by magic: it takes effort.
On established sites, there's enough activity and enough high-quality, highly-viewed content that most new users can quickly twig how a site works and what is expected. On a young site like this, the majority of new users won't spontaneously infer SE's standards, expectations and quirks - it takes time to build standards and momentum.
It takes seconds to write concise, simple comments like "This question isn't sufficiently focussed" or "It looks like you're not familiar with the basics of [topic] - please show what research you've attempted and why you're having difficulty" or "This answer is speculative. We expect answers to be based on empirical evidence", and they're crucial to setting the standards and tone of the site:
- Obviously, they help the user they're addressed to. Most first-time users of young sites won't yet know the ropes the first couple of times they post.
- They also provide signposting for other new users - reducing the likelihood of other new users making similar mistakes.
- They fix "broken windows". If a poorly written post on an interesting topic has [+3,-2] and no comments, it'll look like a typical example of the standard of this site. If it has [+3,-2] and an upvoted comment saying how it should be improved, it's clear what the preferred standard is.
- Finally, they help the community consensus evolve. Important disagreements become visible, and the community will become stronger for it.
The good news is, during Beta, the rate of new content is slow enough that it's easy to give constructive feedback. Economics.SE currently has 5 questions per day. That's tiny - for comparison, Stackoverflow.com has 5,000 questions per day, Mathematics.SE has 370, and most other "full" sites have 20-40. With posts sitting on the front page for days, points 2. and 3. are particularly important.
Downvotes with no comments are a bit like tutting or grunting at someone in the street. It's normal in busy bustling cities, where there's no time to stop and explain, and where people can quickly realise what the correct behaviour is from all the activity around them. It's incongruous and unhelpful in small, growing communities where there's easily enough time to state what the problem is, and where it's not easy to infer the expected behaviour by observation.
Most downvotes without comments on a young Beta site are a missed opportunity to improve the site. By adding a comment, you'll either help set the standard the site aims for - making other users better users - or (and please do be open to this possibility) prompt someone to point out that, actually, you're the one out of kilter with the community on this - making you a better user.