There are also reasons to believe that watching porn might in some scenarios affect the viewer in negative ways that abstract sexual fantasy does not.
Reasonable people can of course disagree to the scope and accuracy of the above objections, but I'd consider neither fundamentally unreasonable.
Masturbation on the other hand is almost universally considered a normal and healthy part of adult sexuality.
Basically just because someone might find porn degrading to women or morally objectionable, doesn't mean they in any way oppose sex and their own sexuality.
I'm sure there is pornography created by people who want to make it. I'm less sure there are dildos created by anyone who wants to be making dildos (the actual workers, not the boss).
I'm sure some people would find a wife using a dildo as degrading to the husband and morally objectionable. Probably most of the middle east. That certainly doesn't give me the right to call it bad, though.