A 'trigger' setting is not a valid warrant for the 'extreme content' tag, as not everyone will react the same way or be triggered. It also leads down the very stupid path of ultra-preventive cautiousness: where everything is flagged as it could possibly cause something. The causality of a pornographic or erotic poem is more direct and evidential than a poem about a car crash or suicide. With the former they are likely to elicit lust and the search for more pornography, thanks to the limitlessness of the internet, whereas the latter is unlikely to cause its topic. Granted, a suicidal poem can lead to suicidal tendencies in a suicidal audience, but by and large that is the last straw that breaks the camel's back, it is not the direct cause. A car crash poem could conceivably cause a car crash, especially if a driver is reading the poem, but the causal effect is less direct than other themes.
The 'extreme content' is a way to roughly censor media/words/poems that are extreme, not average or 'normal'. However due to different temperaments the classification is far from being watertight: one person's extreme content can be another person's average. As such there has to be a sense of checks and balances for when the 'extreme content' tag is used, which will override the choice or classification of the individual poet in order to maintain the overall 'greater good' distinction between extreme and not extreme.
However should a member challenge the change or removal or addition, they can logically argue why. Not just scream and shout and stamp their feet until their preference is manifested. In this case though, the poem was not overtly describing a car crash or a suicide. 'Left in my car' was it? (This 'controversy' should more than adequately boost reads.)
The actions of Mods are far from arbitrary, as the role requires arbitration: the decisions and actions that disfavour some are the same that support, protect and favour others. The very same actions are taken that can fall in a member's favour or fall against them.