You could also say, in a forum, that the fact that the nedd to capitalize the word in sentences in this forum is not "aberta à discussão", ( although Vanda gives up some slack !).
If something is not a dogmatic concept, that is it's just a matter of personal opinion or it depends on the point of view of the observer then you could say that :
"... é matéria de /depende da opinião pessoal";
"... depende do ponto de vista".
If it is not a consensual subject, whereas there are differences of interpretation one could say :
"... sujeita à interpretação (de cada um/de <someone>).