Sounds good to me...

It has started to rain! I was ready to go fishing, too!
or
Thomas's car is a Toyota. Marta has one of those cars too.

In the first sentence, "too" describes the irony of the bad weather.

In the second sentence, "too" details that Marta has the same car as Thomas.

Depending upon what exactly you are trying to say, it may be better for you to remove this comma. If you mean to say in this context that, in addition to something else, we are all world citizens, then the comma is correct. If you are simply including us in the group "world citizens," the the comma needs to go away.

And all that lengthy explanation on "too", which wasn't even the term in question, considering the inquiry is almost 2 years old? Really?

I suppose it's all a matter of whether or not he, or any one who views this page, would like his English to be grammatically correct. This isn't changed by the passage of time. Your comment, on the other hand, is really just inflammatory, Rex. Enjoy your trolling.

You can't be serious.

Please, read the original post again and try to understand that "too" is just a part of an exemplary sentence to show the use of "world citizen" which is the term in question.
Thus, it doesn't make any difference if there is a comma or not and how that would change any connotations because it has nothing to do with "world citizen" itself.