If we have a conflict between two physical principles – in our case, between manifest relativistic symmetry and realism – some metaprinciples may be useful to decide which of the two principles one should prefer. We should not expect that such metaprinciples give a unique answer – this is an unreasonable expectation. Nonetheless, such metaprinciples may be useful guides, and the may be used as arguments in the discussion which of the two principles is worth to be preserved.
One reasonable metaprinciple is to take into account possible conflicts between the two principles in question with other, independent principles:
Criterion of incompatibility with other principles: In case of a conflict between two principles A and B, it is an argument in favour of principle A if principle B is also in conflict with other physical principles A1, ..., Ak.
For the application of this criterion, previous rejections of the principles A1, ..., Ak because of their conflict with B should not be taken into account.
The idea to take into account conflicts with other principles seems to be quite plausible. It may seem less plausible to take into account conflicts with other principles which already have been decided in favour of principle B. But without this point, the criterion would be almost useless – conflicts between physical principles become known in some order in time, and at least the mainstream of physics usually makes some decision which of the principles is preferable. Therefore, once the principle B is considered to be viable at the current moment, its conflicts with other principles have been, usually, decided in favour of B. (The same holds, of course, for A too.)
In general, the criterion nonetheless prefers the mainstream principle: Even if we try not to take into account the mainstream decisions made in previous conflicts, principles which have been rejected are less popular and automatically considered to be less important than those which have not been rejected.
This criterion, in general, also favours the less general principle: A less general principle has, obviously, less possibilities to be in conflict with other principles.
Principles in conflict with manifest relativistic symmetry:
No such list exists for realism. The claim that realism is also in conflict with quantum theory is proven to be false, by an explicit counterexample – pilot wave theory.
Thus, despite the fact that this particular criterion has the general tendency to prefer the principle favoured by the mainstream (which is relativity), as well as the less general principle (which is also relativity), in our case it nonetheless clearly favours realism.