UCI, for example, seems to have a very well defined notion of human subjects research, and this would clearly meet it.

Let's look:
https://services-web.research.uci.edu/compliance/human-resea...

"Any systematic investigation (including pilot studies, program evaluations, qualitative research), that is designed to develop or contribute to generalizable (scholarly) knowledge, and which uses living humans or identifiable private information about living humans qualifies as human subjects research. See Definition of Human Subjects Research for more information."

Down the rabbit hole to https://services-web.research.uci.edu/compliance/human-resea...

"Research is as a systematic investigation, including research development, testing and evaluation, designed to develop or contribute to generalizable knowledge.
...

Examples of systematic investigations include:

Surveys and questionnaires

"

So far, we got it in one.

I'll skip the part of whether it's generalizable - it's clearly intended to be here.

"A human subject means a living individual about whom an investigator (whether professional or student) conducting research:

Obtains information or biospecimens through intervention or interaction with the individual, and uses, studies, or analyzes the information or biospecimens; or

<The or is about getting PII in more cases, but this study is not getting PII>

...

Interaction includes communication or interpersonal contact between investigator and subject.

...
"

Well, there we go.

Seems a lot more straightforward in various IRBs than you seem to say.
As an aside, lots of IRB's also have mass email policies and are required to approve the text.

Now, maybe Princeton's IRB does not have as clear a definition. I can buy it, in fact!

But honestly, it doesn't seem that hard. If you are going to simulate fake emails to humans, for the purpose of gathering their responses, you are in fact, doing human subject research.

It also doesn't seem very hard to draw bright lines:

1. If you are interacting with people to see what their response is, even by email, they need to consent.

2. Do not deliberately deceive humans.

(You can even modify #2 to "do not deliberately deceive humans without an IRB explicitly understanding and weighing the cost/benefit" if you like, but most of the time, you actually do not need to deceive humans)

It's also really really hard to believe someone went to an IRB, and said "i'm going to survey people by sending them emails from fake people that seem mildly threatening, and seeing how they respond.", and an IRB was like "yeah, that seems okay, it's definitely not human subjects research".

It's up to the researchers to explain precisely what thy are doing in an accurate way. Saying you are surveying websites is totally inaccurate and confusing.

If a sociological researcher was like "whoa, i'm not emailing people asking for their family histories", that would be human subject research. Instead, i'm just "retrieving directed graph data from remote email addresses". I don't think that would go over very well.

Finally, as for not seeing the ethical dimension of their work, there is an easy fix for this (IMHO):
Make ethics classes required.
In fact, in lots of places, IRB's wont' review things if you haven't!