* Your results may vary. Actual numbers largely depend on how the popup is implemented (when it shows up, how often it shows up, etc). And even in the cases where you get increased sign ups, studies have shown that those who sign up via a popup have considerably lower engagement metrics, indicating that they signed up by mistake or they signed up because they thought they had to (note that a sign up, in-and-of itself is just a vanity metric with no meaning if it doesn't lead to increased engagement).
I think the reason you included modal forms in your article is the same reason people are posting in this thread about them: you personally don't like them.
I would say that "substituting your opinion for testing" actually is a beginner web design mistake.
People not liking them is a form of qualitative data. That's the feedback we received from enough people to decide that it was damaging our brand long-term.
Seriously, if I get a modal popup, that is the last time I go to a site. If I happen to get one twice, the site goes into the blocklist.
If that's the audience you're after, cool.
Personally, I don't need the karma of annoying the customers, regardless of how much it may seem to work in the short term. I mean, you might as well be Zynga if you're going to do that.
No company survives in the long term by annoying and/or abusing their customers.
Also, whether it "works" or not is completely orthogonal to whether it is ethical. Reading: it matters.
To deny the potential value of x by categorically defining all the people who you think would respond to x is ignorance at best and most likely just hubris.
Hubris? Sure, if you want to call it that.
Personally, I think that expecting a person to sign up for your site based on no evidence whatsoever is pretty damned hubristic. The message I get is "WE ARE SOOOOO FULL OF TEH AWESUM THAT YOU WILL WANT TO GET SPAMMED BY US DAY AND NIGHT!"
Yeah, good luck with that.
Note that I wouldn't mind nearly as much if the site was clever enough to noticed that I'd looked at 15-20 pages (or whatever) and THEN asked me if I wanted to sign up. But it's never that way. It's always right on the front page, before you can even SEE what's on the site.
There's not a chance in hell that I'll sign up for something like that.