Well, to extend the ship analogy: Twitter seems to believe that they're sinking because the ship is overloaded, so they're trying to improve things by tossing people overboard. I don't mean to make light of the situation; I truly feel for all of the people affected by this.
So, why would anyone want to join Twitter now? Well, the diminished share price could be one reason. If you believe the company can turn things around, and you believe that your contributions would help the company do so, then getting in now and hopefully acquiring some shares or options at the current market price could be a rational move. You'd probably want to make sure you've got a lifejacket (i.e. an emergency fund) handy just in case you find yourself thrown overboard in the future.
Also, working at a company which actually has a deployed product with a high public profile is probably not bad. There are plenty of startups which never pan out. And there are plenty of companies out there with a single profitable cash cow and futile strategic projects searching for the next hit. Or barely running but business critical legacy projects written in Cobol, C++ or Java. Twitter doesn't strike me as particularly bad in comparison.
Also, having had layoffs is not necessarily only a bad thing. Even the best company will end up with a certain amount of substandard, undermotivated employees after a long hiring frenzy. The best thing for everyone is to let them go and hopefully blossom elsewhere.
Being able to say "I worked for Twitter" is and will be impressive to most people regardless of Twitter's future. It's not like future employers will see that on a resume think you're the one who sunk the ship (unless you do something high profile to make your negative impact public knowledge).
So, why would anyone want to join Twitter now? Well, the diminished share price could be one reason. If you believe the company can turn things around, and you believe that your contributions would help the company do so, then getting in now and hopefully acquiring some shares or options at the current market price could be a rational move. You'd probably want to make sure you've got a lifejacket (i.e. an emergency fund) handy just in case you find yourself thrown overboard in the future.