It is polite to put up cut tags and warnings to links in a person journal for spoilers. It's not anyone's responsiblity to protect anyone else in fandom, even though I think that if a community wants to truly "serve" the widest amount of people, they should, as a policy, put a warning up on spoilers. Again, they don't have to, but it's good business.
However ...
If you (generic you) don't want to put tags up, if you don't want to use warnings, or if you choose to make your warnings so vague that it's easy to read between the lines, and then tell spoiler-free people that it's "their responsiblity" and "not my fault," then don't bitch and whine when people defriend or filter you. Don't go into someone's journal who's put a post like, "So and so (or this community) has a spoiler up, so avoid or defriend if you want to remain spoiler free" and complain how rude that is. You're the ones telling us that we need to take responsibility, and it seems like trimming your f-list down to people you know don't post blatant spoilers is taking responsiblity.
However ...
If you (generic you) don't want to put tags up, if you don't want to use warnings, or if you choose to make your warnings so vague that it's easy to read between the lines, and then tell spoiler-free people that it's "their responsiblity" and "not my fault," then don't bitch and whine when people defriend or filter you. Don't go into someone's journal who's put a post like, "So and so (or this community) has a spoiler up, so avoid or defriend if you want to remain spoiler free" and complain how rude that is. You're the ones telling us that we need to take responsibility, and it seems like trimming your f-list down to people you know don't post blatant spoilers is taking responsiblity.