I do this periodically on Nifty and have a couple of times on here. The only time I get upset is when someone tries to tell me how or what I can write, for example: a had someone email me accusing me of politicizing my story Thicker Than Water and that I should write more from a Conservative point of view. He refused to tell how I was politicizing my story let alone give examples but he did start giving me Bible verses. I ended up cussing him out and blocked him. Those people I don't deal with well; however, other readers are just really into the story.
Readers will always question your choices. It's human nature. I've had stories that enraged entire groups of people, who demanded I rewrite whole novels. I ignored them (or told them to f**k themselves). In that same vain, though, it really depends on what's being said. They might be looking for clarification or context you didn't add or took for granted. Most commenters aren't doing it be dicks.
If their comments are derailing you, that's really on you. You should comment about how it'll be resolved in the future with hints of things to come, while keeping notes to address things later. You can easily use such comments to tease your audience and get them wanting to read more to find out what happens. You can also through them off by having random, horrible shit come out of nowhere but is still relevant to the story.
If someone complains about realism, point out that the story is fiction. I've had to do that, myself, a few times. It doesn't hurt to gently remind readers that somethings happen a certain. You may not be an expert in a particular field, your research didn't address certain things, so you did the best you could. Or just say, "That's how it works in my world." Most of the time, they think they're helping, so take it as advice that you either need or don't need, then let it go.
I published Thicker Than Water on here and Nifty, with GA getting the chapters first, and the feedback I got helped with the story as I wrote it. It was fun to tease the readers with cliffhangers, using the nicknames they gave my villains, finding out what pushed them emotionally and used it to develop greater narration and dialogue, and with my commenting back, it gave them more context without spoilers (as my story was heavily influenced by real people and events), allowed me to make things clearer in later chapters, fix errors I made, etc., which made them more dedicated readers who then recommended my story to others.
If you're not wanting feedback, post on Nifty. They can't comment directly to a chapter, and most won't send an email. However, use the comments as a tool to help you be a better writer and get your readers excited about what's to come. Read through the comments on other stories to get a feel for what you can accomplish in your own comment section. If someone is being a dick just to be a dick, block or report them; otherwise, let it go or clarify without spoiling.