Come on, requiring an account doesn't make something "not a free tool".
But "free" still means "free", and "tool" still means "tool".
It is not strictly speaking a "tool" it is some form of SaaS, you have to connect to that site, authenticate yourself, etc.
It is not "free" the sheer moment it asks (indirectly, through your e-mail address) your identification.
That there is "nothing bad" in it is another thing.
Yet the owner of the site is presumably paying for a DB to store all this information. Why?
Usually there is one of two answers:
A) They want to sell you shit, and they need some kind of identifier they can use to unlock content
B) They want to collect info on you to sell to other people
Either way, that's not free. If it's A, I am being asked to invest time in a tool without being told it's potential limitations (there's nothing on the front page mentioning limitations on unpaid accounts), and that's a cost.
If it's B, I'm being data-mined, and companies only pay for data-mining if they think they can turn it into more profit, data-mining costs included. So if I'm being data-mined, it's because someone thinks they can use that data to get me to part with more money at some point down the line than I would choose to part with sans manipulation. That's a cost.
Of course, there's always option C) The site creator hasn't thought about why they need an account system, and made one because that's what all the other cool websites do.
Usually when C comes into play, you can expect account data leakages to follow due to piss poor security practices, and that's a cost.
That's not true in the slightest. I can create as many accounts as I can have email addresses, and I can have as many email addresses as I want.
Robust throttling _requires_ an alternative throttling mechanism that works independent of account information, otherwise I can round-robin between accounts to bypass all throttling.
If you're gonna have that anyway, we're back to "no technical need for accounts".
If they use Facebook login instead of email, how do you plan on getting thousands of Facebook accounts?
B) It's been a while since I last checked, but I don't believe there's anything stopping me from just making shittonnes of facebook accounts
C) Facebook accounts are about 90c each, if you're desperate: https://buyaccs.com/en/buy-bulk-facebook-accounts.php
Accounts are not a throttling mechanism. In and of themselves, they cannot be.
It doesn't do that at all, see here: