I'm not keen on spoilers but I can’t say they have 'destroyed' any books for me. And as much as I'd like to not be able to say this, sometimes they improve my reading.
I feel similarly, in that I think any good book will easily withstand any amount of spoilers, though I generally attempt to avoid them, and warn others when they will appear in my posts or reviews. For now, however, I'd like to discuss a phenomenon with spoilers I call "Begging the Spoiler".
In philosophy, begging the question is the logical fallacy in which the conclusion is assumed in the argument being presented. I think a similar situation arises with the discussion of books, when the presence, or significance, of a spoiler only becomes apparent after the spoiler's existence is identified.
For example, if you read the dust jacket summary of a book you may not think anything of it until someone else who has read the book notes "I can't believe how much of the ending they spoiled in the dust jacket summary!" At this point spoilers or hints of spoilers that you would not have noticed suddenly becomes obvious.
I could present numerous concrete examples of this, but by doing so I ultimately risk spoiling books, and I don't think they are necessary. I'm sure most readers have experienced this phenomenon one time or another with books they have read. So do we do more harm than good by noting how a summary, or recommendation, or review may contain spoilers? Would we serve those we are discussing a book with better if we avoided such warnings?
Obviously there are some scenarios where we should still be careful of spoilers (such as explicitly detailing the ending of a book), but what about when we see a trailer for a book turned film? Or read the back of the book summary of a novel we've recommended to a friend? I think in these situations we do more harm than good by "warning" about a spoiler because in doing so we create the spoiler by mentioning it. Out of context, these "spoilers" are mostly innocuous.
So, in conclusion, if you don't want to spoil something for someone else, don't talk about it, and if you do talk about it, don't even mention the presence of a possible spoiler. And if you are on the receiving end - don't stress about potential spoilers. Don't try to decipher if a random comment is actually a major spoiler in disguise.