freezing does kill a few of the nutrients in some foods but nothing compared to cooking. the way to test enzymes is to see if they sprout again after freezing. the answer is yes for many things. think about the earth and how things still grow after being frozen all winter. and how even embryos can be frozen and turned into a human being. so freezing does not kill like heat does.
I think the explanation people use for the raw diet is partly that enzymes pre-digest food before it goes through the stomach (after which they are destroyed). That would suggest enzymes are important. From what I learned, enzymes are not destroyed by cooling (only deactivated until re-heated), however they are destroyed by heating. That was just about lower temperature though; if all the cells become solid instead of liquid (a.k.a. they freeze) that may have a vastly different effect, Im not sure.
I personally prefer to just look at the results I and others get, and if that's good then the explanation may be interesting but not as convincing. I don't believe enough is known about biology to make interesting predictions based on the theories. Rather, the theories are made such that they suit the results (which isn't very surprising, but not very useful outside science yet). I haven't noticed adverse effects of frozen food for myself yet, except it tastes somewhat less good.