Dogma is not available on any streaming platforms, you can't even buy a streaming copy on Amazon. Even the blu-ray release is out of print and can only be bought for a premium on the secondary market.

The reason is that Harvey Weinstein personally owns the distribution rights to the movie, allowed all of the distribution deals to lapse, and hasn't accepted Kevin Smith's offers to buy back the rights.

So I would say that it is entirely ethical to pirate this movie by any means necessary.