How is this a security flaw? Mobile devices are not meant to be shared - they don't have multiple user accounts - meaning you theoretically are not supposed to give the tablet to anyone else. People can use your FB & Twitter account etc. What the OP wants is a guest account, which I support. But this is a choice Google made, no security flaw.
for a non-technical user, this is a security flaw. You buy a tablet, activate it with your gmail account, and next thing is your private email is exposed to your party guests.
For non technical users the browsing history gets exposed too along with chat logs... I would be a lot more worried about those. Basically the problem would be the lack of guest accounts or guest mode. Every time I let someone use my laptop for browsing I open up an incognito window in Chrome.