There's more to the story of Roman Kotsaba and you can't go just by what he or Amnesty International say about this because both are self-interested or parties parties. You need more sources.
While you can choose not to believe the Ukrainian authorities, they say they found $18,000 in his apartment, which is a lot of money for this region, and they claim he is collaborating with Russian intelligence.
Independently, we know that his employer, Nevskiye Novosti in St. Petersburg, in fact has set up a number of fake "Ukrainian" sites which are in fact pro-Moscow sites disseminating disinformation. It's not clear whether he is involved in one of these war propaganda/disinformation sites which you really can't portray as just "having a different opinion." They are orchestrated, paid, pro-government sites. The businessman reported as behind them by independent St. Petersburg journalists has large Russian Defense Ministry contracts.http://www.interpretermag.com/russia-this-week-the-kremlins-growing-army-of-internet-trolls/#5012
Kotsaba has also appeared multiple times on Russian state media associated with some of the most outrageous face news stories, TV1, Rossiya 24.
So you have to look at content and not be colour-blind to it in the name of free expression, and see if in fact he is knowingly engaged in state-funded war propaganda or even incitement of hatred and violence because that is not ethical journalism, and may not even meet the European free speech test.
This is not a clear-cut case of "war resistance" or "conscientious objection." It's a case of someone charged with operating in concert with Russian intelligence, for pay, to undermine Ukraine by inciting draft avoidance.
This is no David McReynolds.