It's a difficult one to pick apart isn't it. There are plenty in our political establishment and on the right who are trying to exploit the Syria situation as part of the emerging new cold war with Russia. E.g. Boris Johnson calling for protests outside the Russian embassy, as if Russia is somehow solely responsible for the situation in Syria, whilst continuing to utterly ignore our own failings in Syria as well as our relationship with Saudi atrocities in Yemen. The same inconsistency is applied to the accusation of war crimes: Swathes of the right wing press are jumping at the opportunity to make that case against Russia whilst simultaneously attacking the "vexatious" historical Iraq inquiries and completely ignoring Yemen.
However, regardless of the geopolitical manoeuvring and propaganda that is occurring, Russia clearly is guilty of murdering thousands of civilians and should face the criticism, protests, investigations and sanctions that such crimes warrant. They are killing civilians at 8 times the rate of the US led coalition so should clearly be facing much greater condemnation.
Corbyn/Milne seem to be of a strand in the left who are willing to turn a blind eye to Russian atrocities in the same way the bulk of the UK/US population, media and political establishment are willing to ignore our own. So yes, the Greens are more coherent because they condemn everyone equally.