Look startups aren't perfect. You will most certainly work harder than at a large established firm. Your life balance will be no where near as good as at a large firm.

But why are you electing to work at a startup?

1) You are getting some options and have the possibility of a big upside which does not exist at a large firm.

2) You want more responsibility and you will certainly get it in the form of wearing many hats, but you will work harder.

3) If things are working out you will be promoted faster and move your career forward much quicker than most established firms.

4) There are many other points I could make here but arguably the most IMPORTANT reason to work at a startup is to LEARN, and learn you will.

There are tradeoffs with working at a startup, startups aren't perfect. To say that they are much worse than large corps who are scared of key man risk and keep you at an arms length so they can fire and lay off thousands at a time is disingenuous.

Corporations are generally only after profits big or small. You as an employee have a responsibility to make the right decisions for you.

Edit: some spelling mistakes.