Again, it has absolutely nothing to do with the password its generates and everything to do with all of those generated passwords are in one place. If you are so forgetful that you have to write down your passwords, you never put them all in one place ever. That logic is right there with putting it on your desk on a piece of paper. You are betting that nobody will ever get to it even though you have no way of knowing it except you've made it worse because its not just one password to one place, its every single password you have to your entire life.
You seem to think that if you get the database than you get the passwords.... This is not correct. You will now need to crack every single hash in that database, and considering that hash derives from a complex password generated by LastPass the probability of you even cracking one person's password is so low that it basically amounts to zero.
For example, let's say my password from LastPass is: N*&nH839j879h&*N which hashed with a salt in the LastPass Database is say 2fd4e1c67a2d28fced849ee1bb76e7391b93eb12 when hashed with some random salt. Now, the way in which a cracker would go about finding this password is:
First they know the hash, since they have the database. They now need to figure out which string of characters generates that Hash (once they find that then they have your password, or a statistically unlikely variation that also generates that identical hash). They do this by first making some assumptions of your password and using that logic applied to brute forcing certain traditional formations of typical passwords. The problem here is nothing is typical, LastPass uses a weird non-human like password, so basically no assumptions can be made, they need to crack each ascii character in a size up to the max password size LastPass creates (I don't know what that it, let's assume it's 16).
Now let's apply the the number of permutations from the maximum string size and figure out how long it'll take to crack a SINGLE password in LastPass's database assuming they generated a 16-character password.... Hmm not a year, not 100 years, not a million years....Not a hundred million years..... damn this number is getting large... Per password....
How likely is it that that password is yours? Well, how many people use LastPass * AverageAmountOfPasswordsPerPerson
You're right, that's terribly insecure....
EDIT: This is assuming within the billion years LastPass doesn't change their salt.