If it's a long comment it's also likely some commenters are only able to address parts of it - again an inline quote clarifies.
I've never had cause to see it as a warning sign or more likely to be someone scoring points, that's going to happen sometimes with or without inline snippets.
Someone making point with a couple of paragraphs.
Commenter takes one sentence or point to shred, maybe it was a weak example or poorly phrased, to invalidate the whole.
repeat. After a few rounds it's becoming clear they're intentionally avoiding the main point.
Have I just committed the cardinal sin of being wrong on the internet? ;)
But,to be fully honest, isn't it what this kind of conversation is about, ultimately speaking? There is a reason it happens mostly in low-stake contexts: dinner tables, casual conversation, comments section. Places where "bullshit pass" is implicitly granted to all participants. If we are not allowed to pick and choose and distort other's meanings then where's the fun and drama in all of this?
That point of view is getting rarer and rarer, especially on the internet. Which is unfortunate. It has ruined online discourse for me almost completely.
some snippet of text from parent comment
I disagree because x, y, z.
another snippet
This is wrong because a, b, c.
(End example)
Doing so obliterates context from a position, especially long form comments (which is the main reason I’m here) in two main ways. First, the technique rarely reproduces the parent in its entirety, picking out black and white statements that are easier to argue against from a sea of nuance. Second, it cuts up the narrative in such a way that downplays the rationale of a position by either leaving out reasoning, or placing arguments between the reasoning and the conclusion.
Sure, the readers can go back and reread the parent. But when the structure of an argument depends on those snippets (and it almost always does) it becomes very difficult to grok.
Generally I just see it as a big warning sign that the quoter is more interested in winning than learning or getting to the truth of the matter and thus is best ignored.