Revisiting one of my previous statements, I'd like to mention that one of the reasons I joined Lewd was how comfy it was (and still is), and one of the reasons I appraised it as such was the ease with which I could create my account and start posting. Certainly, email logins are markedly more secure, but I'd never even heard of them before reading this thread. I can say with surety that, if such a system were implemented previous to my discovery of Lewd, it would've confused me enough that I wouldn't even bother returning after a while.
As an aside, I'd also like to point out that if such a system were implemented, it'd probably resemble Google's uber-annoying two-step verification process. Sure, you wouldn't have to remember a password on paper, but that only applies when you're on one computer and using one browser. Imagine if you've got multiple browsers on multiple machines like me; every separate login means yet another trip to my inbox. If it's a chore for dedicated users like me, then new users are likely to deem it a waste of time, and leave for greener pastures.
It's kinda hard for me to find words right now, so I'll keep it short: Implementing email login as the default (or only) method to access Lewd is an incredibly bad idea, simply because most people aren't used to it. As such, we ought to maintain the traditional username-and-password login by default, and offer the new method as an optional layer of security for anyone who's interested.