the irony here... bitcoin is essentially an altcurrency... just as fiat currency was an alt to silver/gold/etc... (and as another mentioned there are plenty of alt fiats)... and just as metals and gems were alts to whatever we used before them to facilitate trade... it's all just an evolutionary part of our interactions. and if there's one thing humans love to do, it's create... the copy stage is just a natural part of that process... copy - create - learn - innovate

so, here's a real question: Why the hostility? Are these cryptocurrency experimenters hurting you? This is just a ride. We're experiencing an evolution of something... How about an alternate perspective (bear with me here, i know how you feel about alternates   ) : Many altcoin creators may just be experimenting, learning something new, perhaps even new to programming in general... so they dive into creating their own altcoin for whatever reason... they make mistakes, some creations meet an early end, they try again... time goes on and the inexperienced become experienced... through trial and error (knowing how things can go wrong and how to fix it can be very helpful) and a genuine desire to create something of their own (one of the most powerful internal motivating forces we possess)...

Now they're ready to offer improvements to Bitcoin.  

So to answer your question of what these altcoins offer that bitcoin and litecoin don't: mistake-fodder. There's a reason medical students practice on cadavers before becoming surgeons... why pilots practice in flight simulators before actually flying a plane... why divers practice in pools... or rock climbers on walls with harnesses......... i can't think of anymore...