Should the U.S  annex all islands on the caribbean ?

Only if said Caribbean islands want to be annexed. The US cannot just annex whatever it wants to.

The USA is behind the curve. All the annexing was done well over 100 years ago, several centuries ago in some cases.

No, the US doesn't have the right to do that.

Perhaps pay attention in school next time. The US can't simply annex foreign countries. 

But even that, why would the US want to do that? Most Caribbean islands are relatively poor because they lack natural resources. Tourism is by far the leading industry. Adding all the islands to the US would simply cause more money to flow from current tax payers into the Caribbean in welfare and other social programs. In addition, there would need to be a large increase in military to protect those places without really any strategic benefit.

So I don't really see any benefit of doing it even if the US could. What am I missing? What would the US get out of it?

No of course not.  Why would we resort back to colonialism?

thats up to them

heavens no !!!  Have YOU ever been to Haiti ????