and again, the franchise goes on to show that the future CAN be changed, so...
The theory of the complete causality loop, with no ability to change, works great if you only look at most
of the first movie, and even then, only if you want to accept it as-is, and without thinking about how that situation could have come about.
From my POV, that's all well and good, but and actually fits with how I see things as well, as long as you accept it's not the first time through this particular loop
The 1st movie alone can be explained by either theory, give or take, but when the later movies come out, the 'can't change the future' theory has to go out the window, unless you want to start playing the "this and that aren't canon" game? Since you'd have to exclude dialog from the 1st movie itself, seems a poor argument to start from