[lapser]

A long time ago, I was still in college (UK college, i.e., pre-university), and still learning.

I discovered a classmate was involved in some event, and found the event's website. They didn't have a captcha. By your logic, this was the right choice.

In reality, my dumb ass decided it would be fun to script something that would register millions of users (another classmate ran the script with me). After a few hundred thousand registration, the website was brought to its knees. I was a bit shook, but didn't think much of it.

Next morning I come into class, and was reprimanded by my teacher. Turns out, the owner of said event had threatened to sue the school and me, among other things. What had happened was their servers were down, their email server was brought to its knees, their web servers had died, and generally I had caused a lot of damage without even thinking about it. It caused them to potentially lose some money. None of this was my intention, of course, but I didn't know much better.

Point is, kids will kid, and spammers will spam. There are plenty of bots that just scrape the internet and fill out forms indiscriminately.

Captcha may or may not be the best option here (I'm always of the opinion it's not, especially not reCAPTCHA), but something has to be put in place, even if to stop the majority of bad actors.

[asddubs]

you can also just limit the amount of sign ups from one IP each day. There's more simple heuristics to prevent unsophisticated abuse like that

[Quarrel]

You can, but then you discover that places like Bangladesh and Cambodia, that do a fair bit of freelance work on the 'net use a surprisingly tiny number of IPv4 addresses to do it.

For lots of these countries their total allocation of IPv4 addresses is < 20 per 1000 people and the nature of their access (through glorified internet cafes) mean that you will have some IP addresses that really are totally legit, yet have LOTS of users.

One size fits all is very dangerous on the Internet.

[CWuestefeld]

No way. In the B2B world at least, I expect hundreds of users coming from behind the same corporate proxies.

[distcs]

> you can also just limit the amount of sign ups from one IP each day

This is a classic example of how "just do this" kind of thinking can lead to terrible results.

Do you now see how "just limiting the sign ups from one IP each day" can go very very wrong?

[hansvm]

> limit the amount of sign ups from one IP each day

one per library per day...