Bad SEO is like bad student poetry: they're looking for words to fit the rhyme (or algorithm) instead of looking for the words that MEAN something to people.
There's nothing wrong with using search traffic records to figure out what words people tend to type when they're searching for the topic you're writing about, and then USING the same terms that your particular audience uses. That's finding a common language.
There's nothing wrong with using search traffic records to figure out, "Hey, a lot of my visitors are coming to look for X and Y, so let me make sure my page is ABOUT X and Y and answers their questions. Or, if that's not the right audience for my content, maybe I need to use different language so that search engines send the readers who really ARE interested in what I have to say."
In both cases, you have something to say; you're just looking for common language with your readers.
Bad SEO is when you don't have something to say and chase popular searches.
Bad SEO is when you don't know what you're talking about, so you use SEO to try to trick people into visiting your page when you don't, in fact, have the content they're interested in.
Good SEO is like having a really great coffee stand, then using clever marketing and a cute, easily-visible sign to help people find it.
Bad SEO is like selling really AWFUL coffee, then paying people to shill about how good the coffee is and sticking "come try my coffee!" flyers on every car parked in a ten block radius. Sorry, you gotta start with having good coffee (i.e. good content), then it's okay to use fun marketing techniques to help attract coffee drinkers.