Well If it's only dangerous if someone has access to my computer, wouldn't that make the keychain or third party software with a similar purpose, obsolete? Assuming I'm 100% sure that nobody else would ever physically use my computer.
While GG is correct, you should always have a password on your Mac. This would require you to login when you open the keychain app. Now if someone knows your Mac password then that is a different story. In this case, apps like 1password can have their own password separate from your Mac password; hence, they would need to know that password to get all your information.
All in all, like I said before and as GG also mentioned, chances are very high that it was your email account which was hacked and not your computer. Use gmail as it seems reliable for the reasons outlined by GG and make strong passwords. To give you an example, my bank and email passwords are all over 10 characters long, use upper and lower cases, numbers, and special characters. While they may be hard to remember at first, you'll get good at it.