If the user is in the sudoers file, they are authorized to do the things configured there.

Correct. But the thing configured there is "to act on behalf of root for these items", not the "things" themselves.

Which is obvious when they can do the thing after entering their own password.

$ touch file1
$ sudo touch file2
$ ls -l file{1,2}
-rw------- 1 illecors   illecors   0 Nov 12 14:56 file1
-rw------- 1 root       root       0 Nov 12 14:56 file2

It is not you executing stuff with sudo. file1 is owned by you, but file2 is owned by root.

But since they already entered the same password at login, and are still logged in, there’s no point in entering the same password one more time.

There is a point. See above.

The argument “a password prompt tells the user to stop and think” is wrong.

That's not an argument I've made, nor make.

For that, you can pop up a confirmation dialog, or even a text box where they have to type in “yes”.

Both of which are much easier to defeat than a pop up confirmation dialog with a text box for your password.

Using a password for anything other than proving the correct user is at the keyboard makes it less secure.

No it doesn't - you seem to be making things up to justify your lack of understanding. Authentication is not the same as authorisation, nor should it be treated the same way.

When you type in your password on a login prompt - you authenticate who you are.

When you type in your password on a sudo prompt - you authorise a command to be carried out on behalf of root.

This is why Active Directory and Kerberos are so great. You log in once in the morning, and that’s it.

I'm not sure you realise how little you do on a windows machine. Good luck installing system software or altering system files on an AD managed Windows machine without authorisation. Which is what your meme(?) is implying.

And since you only have to type in your password once before work, it can be really secure and long.

There is no justification here, just a manufactured statement.

Also, the chance of someone standing behind you while you type it is reduced.

See above.