I've seen (and have done myself) someone ask a question and the answer or a remark made afterwards may have "spoiled" a part of a class story...like a betrayal..a merging..an end boss...etc...even if the person saying the "spoiler" wasn't doing so out of malice or intent to "spoil" anything..just responding/answering...
If you're answering a question in general chat that could be considered a "spoiler" then you can easily answer the question by sending a whisper to the person asking the question rather than broadcasting the answer in general chat.
The makeb quest probably shouldn't be triggered until you finish your main class quest.
They can't really do that. Makeb isn't a class quest. There are people who leveled to 50 and never finished their class quest and didn't really care that they didn't finish it. You couldn't tell people who bought ROTHC and were at level 50 that they couldn't do any of the ROTHC content unless they finished their class quest. If a few people don't pay attention and start up the Makeb questline before their class story is finished, then so be it....but that's better than gating the content.