It's the circle of life. Dynamically typed language has fans. Other people correctly say that it would be a lot more useful with static types. Fans take this personally and say it doesn't need static types because (they aren't useful anyway/it goes against the spirit of the language/it's only a scripting language anyway/you can just use a debugger/static types hurt productivity/etc. etc.)
Then eventually they add static types. Happened to Python, JavaScript, Ruby... I'm sure there are more.
For my $0.02 - it depends where you want to put the onus
Statically typed languages put the onus on the caller to transform the data into the shape(s) required.
Dynamically typed languages put the onus on the called to handle anything.
That is, in a dynamically typed environment your function has to defensively code for every possible type it could be handed.