Reddit is a hivemind that believes only in the current politically correct view that is usually dictated by US and Europe. They let their feelings to play an important role on the weight of an argument, that's why they like to vote other people's posts based on how they feel about it. Currently most people are shocked by the tragical events in eastern Ukraine and they want to find a target to let their anger out on, and Russia is good choice for that. Comment like «Fuck Russia» encapsulates all this confusion and frustration people feel regarding the subject by directing it towards most plausible target of hatred people have, that is Russia. The comment is simple enough for everyone to understand, it has the lowest common denominator (Russia) that everyone can join it and it's vague enough that it doesn't really mean anything but people still can feel like they have contributed to something meaningful. It's still stupid comment in its generalization when in truth not all of Russia or Russians should be fucked, to use their terms, but at times like this when people are furious they feel they are justified to spout out things like that and that there is no requirements to base their opinion anyhow as it's accepted by the majority, simple high contrast «us and them» thinking.