I can’t really tell whether taking cellulase is bad.
It does destroy cellulose. But cellulose is a natural part of vegetables, fruits, grains and various other seeds. Our body never evolved the capability to digest cellulose, so I guess digesting cellulose is not necessary at all. That does not automatically mean that taking an additive (cellulase) to digest cellulose is necessarily bad. It does of course have the disadvantage that is reduces the amount of fibres in the intestinal tract. It is well known that undigestible fibres are necessary for a correct functioning of the intestings, and for producing a good stool.
So by taking cellulase you are reducing the amount of fibres in your intestinal tract. There is slack, of course, because you generally eat other fibres as well. But given the fact that the average person (which you are certainly not) is too low on fibres, reducing fibres even further would surely be a bad idea for the average person.
And, indeed, cellulase transforms cellulose into sugar (glucose). Is that a problem? I cannot tell.
Sorry for only being able to give you my random thoughts. I would have liked to give you something more similar to an answer, but my knowledge is simply too limited. Knowing the limits on my knowledge, I think it’s better not to pretend I have knowledge I don’t really have.