Destiny Players Who Don't Buy the Expansion Get Some Old Content Locked Out
If you purchase Destiny but not The Taken King expansion, you can play the original game content but you can't play the new stuff included in the expansion — that makes sense. However, Destiny players (who didn't buy The Taken King) reported that some of the content in the original game became unaccessible.
"On September 14, anyone with a copy of Destiny could play a variety of crucible modes or take on the nightfall and weekly heroic strikes; as of September 15, they can't," Kotaku wrote based on players' complaints on Reddit and Destiny forum (you can see what are locked out at this Reddit post).
Bungie didn't mean to punish players for not buying the expansion, and it's because the expansion had large amount of changes and upgrades to the original game and therefore, some stuff was added and some was removed. Bungie didn't tell the community what exactly and how much would be removed and it brought complaints.
Related article: Destiny The Taken King Review