Skye-N-Rain:
There will be a more button soon. The thing is that some tags can also be spoilers...
If I remember correctly, I never received tags like main lead death. Users are, usually, not set on spoiling the show for others. Most tags are just general tags (Highschool / Time Travel). If you did not watch the drama/movie and only saw 1-2 word-length tag, it would not spoil anything, even it was a spoiler, you would not know since 1-2 words are too general and you did not watch the drama/movie.
Example, let's assume I added "suicide" to a drama/movie tags, you would not know if it happened at the beginning or end, or if it is a spoiler or not since you did not watch it. However, even if it happened at the end you would not even remember the tags while watching (it is not like a checklist you keep going over while watching). But the important thing is that you warned people who are sensitive toward topics like suicide.
I have been using the tags in the manga website, for years now, and I have never been spoiled at all. They are mostly used for the search, not relay the entire plot. Moreover, almost all the tags added by users are from the synopsis or first couple of episode (most of them included a note saying that). We can always add a note under the tag box, to ask users not to add spoilers. In addition, no one bothers reading all of the tags, they are mostly for people looking for a specific thing in a movie or drama.
The presumable problem of spoilery tags, would not be fixed even if we add pre-accepted tags, cause that also can be done in 1 step, instead of 2, when monitoring while approving.
Also, if it is about spoilers, why don't we remove the "Tragedy" genre? This is the biggest spoiler we have since you know one of the main characters will die.