The assumption here, and its a reasonable one, is that when you buy their product, you want to have all of the features it offers. That includes the software package. It's not for everyone and it isn't required.
Annoyances with GE over the years are things like using it to optimize a game, then playing it and changing settings yourself later, only to find that GE changes them back again at a later time (if it is specifically set to optimize automatically).
Scanning for all of the games present on the system upon launch can cause the program to take forever to load up. The bulk of my library is on traditional hard drives, so I feel it.
I already had a login since I participate on the geforce.com forums. It's handy for the latest information on driver details / bugs / driver hotfixes, etc. The login's needed to be able to actually post what bugs you might encounter, rather than simply lurking and reading about it.
You also need the login if you intend to share your gaming experience with others. That's done in multiple ways like broadcasting to twitch, youtube, etc, and linking to the accounts on those sites. It just makes sense to have that broadcasting information protected behind a username and password.
Speculating here, if you are a content creator of any kind, especially with the new software available with the Pascal line, having that original work linked back to the creator through username / password is especially handy. In this case, you want there to be meta data that links you back to the originals.
I have nearly everything in GE disabled, it doesn't doesn't scan for games daily, it doesn't optimize any, it doesn't automatically download driver or GE updates, it simply records 20 minutes of gameplay at the highest quality, continuously for my convenience.
tl;dr - I dont have a problem with logging in because I already had a geforce.com username.