The detention facilities are very obviously concentration camps. Such camps existed before and after those concentration camps that are most commonly associated with the term, those in Nazi Germany. And not all of Germany's concentration camps were death camps. They called the various types of camps by different names, but all would fit the description offered by the Merriam-Webster dictionary:
"a place where large numbers of people (such as prisoners of war, political prisoners, refugees, or the members of an ethnic or religious minority) are detained or confined under armed guard."
Merriam-Webster itself goes on to say "especially" the camps associated with Nazi Germany, but the term is not exclusive to the Nazi death camps.
I believe the description fits our southern border detention centers as well.
Some people reject the use of this term because they 1)mistakenly think such camps have to be death or extermination camps to be called concentration camps, and because they 2) do not want to accept that the United States would actually operate concentration camps. They do not want to associate their country with that term. They call it an overreaction, but it's only because of the automatic and default association with the Nazis that the association creates an immediate rejection by some. Do not associate that term with this country. We are not like the Nazis. Drop the automatic association, and it's just a term denoting the type of place described by Merriam-Webster.
Making believe we cannot call them concentration camps does not change the reality. AOC used the term in order to call attention to them, I'm sure she knew she would get attention for doing so, and her use did call attention to the detention centers, and to AOC herself. Basically, it forces the issue by causing Americans to say "are we really doing this? Is this who we are?" It forces us to look at ourselves. Which is exactly what AOC was aiming for. Just my two cents....