I don't go around like the "niceness police", but I do make it a point to support people and institutions that value kindness to others. I only shop where I am treated nicely, and I don't eat in homes where a well-known hechsher is served with a dose of unkindness. My husband, by the way, thinks I'm crazy. But why would I trust the kashrus of people to whom human dignity means so little?
I've wondered about this too. Fox's approach takes it out of the aesthetic realm ("these people make me want to puke") to a halakhic one. Also, it correctly treats the situation as the problem of the nasty folks instead of a problem of the people who want to avoid them ("it's my problem, I puke too easily").
So what's the halakhic situation? We're not supposed to trust the kashrut of people who aren't shomerei mitzvot. The criterion is usually that apparent shomerei shabbat are trustworthy on kashrut. Can we use other criteria?
An anecdote. I once had Shabbat lunch by the Whoevers (not their real name); one of the Whoevers and some of their guests spent a lot of time griping obnoxiously and maliciously about some neighbor of theirs who in nice weather spends the day sitting on the porch with her bare feet on a chair. In the uplifting version of the story--a version I never tell anyone because it didn't happen that way--I say, "Who cares? It's not like you're saying she spends her time doing malicious gossip or something that's actually serious. And this is all lashon hara anyway. You persist in your gossip? A bentcher if you please. Good day to you [harumph]."
But that's not what happened. (These quotation marks are gisties, not verbatims.) After a bunch of this stuff, one of the gossipers said, "And remember when the Ifyouwills' son's bike was stolen? We were all sure her son"--the son of the object of the gossip--"had taken it. It turned out someone else did. But we were so sure her son did, which just goes to show you how disreputable she is." At this point I finally protested. "Excuse me, but the fact that some people were sure her son stole it doesn't reflect badly on her; it reflects badly on those who hate her so much that they assumed this about her. And the really sad and absurd part is that some people are still using this as some sort of indictment of her."
I didn't respond until this hoohah had reached a high threshold of absurdity, and I was responding more to the absurdity than to the malice in the air. I don't come off well in this story.
I wasn't invited back, which is good because it saved me the trouble of coming up with wimpy excuses for declining the invitations. But the question that's been bugging me is similar to the one that Fox eloquently raises--"Why would I trust the kashrus of people to whom human dignity means so little?" Fox makes it into a halakhic issue, not a matter of mere dislike.
I am not a halakhist, so all I can offer is a bunch of questions. As Hillel said in Babylonian Jewish Aramaic. "If you can't take it, don't dish it out." Yonatan paraphrases this and uses it as his gloss on ve'ahavta lere'akha kamokha--love your associate like yourself. In what I believe is a nonhalakhic statement, we're told this is the most important law of the Torah. Does the behavior described above violate ve'ahavta lere'akha kamokha? If so, does the violation of the most important law render questions of shemirat Shabbat irrelevant? I mean, it means they're not shomer mitzvot on the most important mitzvah, right? But OK. Let's say the ve'ahavta lere'akha kamokha approach is a nonstarter. We hear that there's not supposed to be hostile talk on Shabbat. Is this halakhah, or is it just pious stuff that we say to each other? If it is halakhah, is malicious gossip (or any other malicious speech) a form of chillul Shabbat, in which case we can distrust their kashrut on Shabbat grounds after all?
If you have insights into any of this, I'd appreciate your comments. Don't worry, I understand that you're not my local Orthodox rabbi and I won't take your word as law.