I think that this can be answered by backing up and pointing to some fundamental Stack Exchange concepts. (Since you're not citing specific examples, I'm answering this in a broad, general way. If I'm covering stuff you're very familiar with, I apologize if it comes across as lecturing or talking down; that's not my intent.)
Stack Exchange sites are not web forums, whose job is to encourage a happy community that will come back and keep the site running through ad impressions. I'm sorry if that sounds harsh, but it's true. The purpose of a Stack Exchange Q&A site is not to provide a forum for people's questions, or even to help people. The purpose of Stack Exchange is to make the internet a better, more curated place, with lists of on-topic questions where the community votes the best answers to the top of the page. We want to ask and answer questions so well that when you Google "How do I fix [problem] on my [type of bike]", that Stack Exchange question is the first hit on Google. Furthermore, we want to be viewed as a reliable resource. (That last is very important.)
Communities are provided with the close and delete mechanisms to ensure that questions that are off-topic, or unanswerable (i.e., can't be answered definitively and voted on) will be removed from the site. Closing a question disallows further answers, so the question can be edited. If the question is beyond saving, it can be deleted. Of course, individuals will disagree on what questions are good ones. This helps make the question more reliably answerable with answers that can be voted on.
Closing is not unfriendly, nor is it malicious. Think of editing a letter: Would you want to edit a letter as the replies came in? Of course not, you'd want to edit it before it's sent out. Similarly, it's worth noting that, when borderline or problematic questions are closed quickly, they can be edited with a freer hand than if they're left open. If they're left open, answers pile up, then it makes it harder to edit the question into a good one. "What bike should I get" may be edited to "What features should I get in a winter commuter bike". If the more general question is answered, it's a waste of everybody's time.
In order to encourage good content and discourage bad content, users are also provided with the upvote and downvote mechanisms. Upvoting good content is a way of telling the system, "this person does good stuff here. We can trust them." Similarly, misinformation needs to be voted down, or the site will fill with it over time. Downvoting is a deterrent that needs to be exercised or Stack Exchange won't work.
Now, to the meat of this: Leaving feedback when downvoting is undeniably helpful. Downvoting someone's question or answer without explaining why leaves them to guess at why they were downvoted. It feels like a slap, getting a downvote like that. Requiring users to leave a comment while downvoting has been discussed on Meta.SO. However, filling out a comment to fill out a comment seems pointless, and it's important to preserve voter anonymity.
As long as most users are leaving constructive feedback, I think we'll be fine. Drive-by downvoting is, as far as I can see, the exception and not the rule.
If the downvoting and enforcement is just the random acts of trolls...
It's easy to feel this way when you see a question closed. And I would agree that responsible downvoting and closing should be accompanied with comments explaining how the question can be improved, or it's worthless. (However, I also feel that anonymous downvoting is desirable. But that's another discussion.)
If you feel that "enforcing" is a bad thing, perhaps Stack Exchange isn't for you. This is not a feee-for-all discussion forum, it's a place meant to generate good, worthwhile, structured content that will improve the internet. People who downvote and close questions are absolutely required, and calling them "trolls" dismisses their contributions to the site. They are encouraging good content by taking these actions. Rather than worry about the few anonymous downvoters, simply encourage constructive feeback by listening and responding to it. And viewing closing as an opportunity to edit and re-open will result in better questions and answers.