Similarly, an earlier verse seems diminish the importance of the Seventh Day Adventists' distinctive belief in vegetarianism.
For instance, one person believes it’s all right to eat anything. But another believer with a sensitive conscience will eat only vegetables. ...those who don’t eat certain foods must not condemn those who do, for God has accepted them. Who are you to condemn someone else’s servants?
(FYI, NLT has a more favorable translation. E.g., instead of "sensitive conscience", NIV says "whose faith is weak". But even NLT begs the question: does it really matter to God?)
The Biblical Research Institute of the General Conference of Seventh-day Adventists has a fairly extensive analysis of these verses. It was written by the department chair of Theology and Christian
Philosophy at Andrews University (Seventh-day Adventist affiliation). I recommend reading the whole thing.
The short version:
Paul said something similar about diet that he also said about days. It's hard to tell whether there was a specific contention over diet, but as in other epistles, he is asking for more consideration from mature Christians towards their weaker brethren. Days should be viewed in the same spirit.
Paul is not trying to say there are no commandments, that "everything goes". He is not discrediting the Ten Commandments. He knows they are holy (Romans 7:12). That the Christian reader knows the indisputable value of the Ten Commandments (including seventh-day worship), is taken for granted by Paul.
Paul was likely talking about Jewish feast days. If Christians want to observe them, fine. If not, that's fine too.