Of course, you tacitly skipped over the other helpful comments and instead chose to concentrate on the worst comment in that thread. However, that doesn’t render the message delivered there wrong in any way – read the whole article/how-to before starting, just as you read the whole recipe before starting to cook.
So, yeah, you
a) didn’t read the manuals supplied with your distribution
b) instead went directly to a random third party site via Google
c) blindly trusted said site without fully reading it
d) messed up while doing so.
You should have gotten a computer-literate friend to help you, just as you don’t fix your car by looking for an howto online and dismissing the manual you can usually find in the glove compartment.
The thing is, of course I know I screwed up. I don't need you or anyone else to tell me that. I already know it.
But that has nothing to do with my complaint: the top match for a Google search for "ubuntu add user" is a site that gives out poor quality information, doesn't improve that information as a result of user feedback, and has a community that is positively hostile to feedback. Yes, as you point out, there were also helpful comments in that thread. There were also several other people who had the same problem I did, and the site never did anything to improve its content.
Isn't it obvious that this was a lousy tutorial? Doesn't the author of a site like this have any responsibility to put out useful information? Does the fact that I screwed up make my feedback any less valuable? If you're writing tutorials, that's exactly the kind of feedback you ought to be looking for, so you can improve your tutorials.
Contrast it with Arch Linux's page on user management:
Here they do use the same useradd command that I was complaining about (probably because Arch doesn't include adduser by default?), but they give a complete example with all the options required, followed by an explanation of those options.
Now that's how you do it.
But we're all newbies at something, some of the time. In my case it was basic Linux user setup.
Maybe you even screwed something up once, as a result of somebody giving you bad information that you didn't thoroughly check out. (Not saying you did, just possible.) If that ever happened, which would be a better response from the source of that information: chewing you out thoroughly, or correcting the bad information?