You absolutely can measure an octave or decibel. It's just a relative quantity, in just the same way any quantification of orientation is relative.
(For example, you can measure an octave by marking out a particular fret on your guitar; it will make an octave change whichever particular note you start with.)
You can feel free to "reject" whatever you want. You'll just be wrong/confused. ;-) (But you'll be in good company. Most working engineers, scientists, and mathematicians don't have or need a particularly clear philosophical understanding of angles.)