I feel like the writers have forgotten about the whole 'the world is full of radiation' part of the show like at the beginning of season 1 they would have glow in the dark plants and mutant animals etc. Now we see normal looking horses and no indication of anything being radioactive in the show. Its completely become about the clans and war and now right after ALIE theyre fighting to save everyone from yet another nuclear apocalypse. Im also really pissed that Clarke wouldnt look at Finn for killing 42 (i think) grounders when he wasnt even going to the village with the intentions of killing, but if Bellamy goes with a team of people with guns and massacres 300 people that were PROTECTING them its alright because its Bellamy and he made a mistake. Everyone seems to be accepting Bellamy straight after this fact and thats really stupid.
Yes Clarke couldn't look at Finn after he killed the grounders. But that was the start of the second season... they were still trying to build up the alliance with Lexa and TreKru and the worst thing that had happened so far was the drop ship explosion (which is kinda minor compared to everything else that has happened). Also the last time she saw Finn, he was the peace maker of the group, always trying to keep the alience, seeing him kill the villiage of grounders was so out of character it changed the way clarke saw him.
She was better with Bellamy because he has always been unpredictable and she had been through the whole Mt Weather lever situation killing over 300 people and she then became Wanheda. She became a lot tougher in season 3 and had more of an understanding as to why Bellamy did what he did. Yes what he did was wrong but he is still trying to make up for it now even during season 4