The problem is not with spoiler tags. All they do is give the reader a little more information about what they are reading and help them decide how much more to read. Over use of spoiler tags (one for each season in the plot summary of a character, for example) can look bad and is unnecessary in a well written article, but generally spoiler tags serve a useful purpose.
The problem is with trying to avoid giving away spoilers. We shouldn't be worrying about that unless it really makes no difference to the quality of the article. Write a good article, then worry about adding spoiler tags. If a spoiler has to go in the lead for the article to work, then so be it.
It is worth mentioning that it is possible to warn readers about spoilers without spoiler tags. Just start the sentence "In season 3, it is revealed that...". Yes, if you're reading fast you might end up reading the spoiler before you've realised what you're doing, but it's much better than nothing and can be used in almost any situation. Spoiler tags only really work when the part with the spoilers is naturally separate from the rest of the article.
Oh, and "click here to see spoilers" is a very bad idea - for a start, I don't think it is standards compliant. Secondly, Wikipedia is not designed to be read only online, its designed to be available for anyone to use in any way they like - how to you parse a hidden spoiler when printing articles out?