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I think you misunderstand the GPL ideology (to use your words).

The idealogy is that proprietary software is wrong, bad, unethical. Software freedom should be available to all.

The copyleft terms of the GPL are a tactic a means to defending software freedom. And to that extent, all the incompatibility with other free licenses are indeed a bug a downside, a hampering of freedom in practice. That downside is accepted because of (and only when it is) the judgment that it is a net gain for software freedom anyway because it frustrates the development of non-free software.

There does not exist any ideology that wants incompatibility between free software licenses. It is a price that some feel should be paid sometimes in order to be incompatible with non-free licenses which are the actual problem.