First, try good grammar. All A are B is just bad grammar. You should say: All A's are B. That is, "all" implies a plural here, whereas in "A is B", "is" implies a singular.
An example of A is B may be: Joe is Irish. That is, one thing, Joe, has the one quality, property or attribute of being Irish.
An example of All A's are B would be: All Irish Catholics are Irish.
Please note the difference with for example: The population of Irish Catholics living in Britain is quite large. That is, the population is quite large, not necessarily the Irish Catholics themselves. So, it is an instance of A is B, not All A's are B.
The form A is B is also used to say, for example "Superman is Kent Clark". Here, this is a relation between two things, not between a thing and a quality, but we can also do good logic with that: "If Superman is Kent Clark, then, if Kent Clark is hungry, then Superman is hungry, too". The word "is" here is used in the two different ways I just explained but, in spoken languages, we are seldom confused as to which is which because the context usually gives us the necessary clues.