There's really very little excuse for not knowing enough front-end stuff to consider yourself a "full-stack web developer".
HTML/CSS are easy-peasy, and while some people don't like Javascript, it's hard to get away from and you can only increase your value as a developer by being able to work with it. Add to that a little bit of client-side tooling knowledge (Gulp, SCSS/LESS), and some familiarity with jQuery and you're good to go. Shouldn't take more than a week tops to get the hang of it all; no-one's saying you have to be a wizard.
You don't have to love front-end work (I enjoy it, but I also really like doing back-end work so I understand both perspectives), but you're doing yourself and anyone who employs you a disservice by not being at least a somewhat-solid front-end dev. Early-stage startups don't really have room for people without that level of versatility. If you're going to write code, you should be able to write front-end code, back-end code, and be able to administrate your startup's servers to some degree. If you can only do front-end, you'd better be at least a decent designer. If you can only do backend, you ought to be doing some kick-ass ops work. The phrase "T-shaped individual" comes to mind.
While amazing generalists/full-stack guys are great, having very strong individuals own a particular domain of the code can have its benefits as well. Sure, you miss a bit of oversight, but when you're in the building phase and you just want to Get Shit Done, it helps if you don't have someone else mucking around in your code while you're building it.
Absolutely, hence my comment towards the end about having T-shaped individuals. I worked on a startup team recently where responsibilities were pretty cleanly divided: I worked on the front end, and a coworker worked on the backend.
Both of us were much stronger at our chosen domains than the other, but we were also both strong enough on the other end to fill in any gaps. If we were doing mostly front-end stuff for a sprint, he was able to jump in without me having to worry about it, and vice-versa.
IMO, that's the kind of full-stack developers that early-stage startups (that aren't specifically tech-focused, eg language processing) need.
HTML/CSS are easy-peasy, and while some people don't like Javascript, it's hard to get away from and you can only increase your value as a developer by being able to work with it. Add to that a little bit of client-side tooling knowledge (Gulp, SCSS/LESS), and some familiarity with jQuery and you're good to go. Shouldn't take more than a week tops to get the hang of it all; no-one's saying you have to be a wizard.
You don't have to love front-end work (I enjoy it, but I also really like doing back-end work so I understand both perspectives), but you're doing yourself and anyone who employs you a disservice by not being at least a somewhat-solid front-end dev. Early-stage startups don't really have room for people without that level of versatility. If you're going to write code, you should be able to write front-end code, back-end code, and be able to administrate your startup's servers to some degree. If you can only do front-end, you'd better be at least a decent designer. If you can only do backend, you ought to be doing some kick-ass ops work. The phrase "T-shaped individual" comes to mind.