I think we should treat the question of how political prisoners are treated, and whether they're killed in prison, independently of whether we approve of their politics. Navalny's politics may not have been attractive, but this is still another example of Putin imprisoning and killing his critics, and that is what it is no matter where the critics are coming from politically.

I was just reading a thread about Julian Assange, another prisoner whose treatment is politically motivated and whose politics we may not like, and people there are saying they don't care how he's treated because he was acting as a Russian stooge. We're in danger of losing track of the difference between our moral view of an individual and the question of human rights. Rights should apply to everyone, nice or nasty, and leaders who abuse their critics should be held responsible, no matter whether we like or dislike the politics of the leader or the critic.

He was also a Russian fascist with well documented association with the neo-Nazis in the early 2000s then turned into a pro-Western liberal who opposes Putin.

Edit: 2011 NY Times profile about Navalny (CW: racism):

Liberals, meanwhile, have deep reservations about him, because he espouses Russian nationalist views. He has appeared as a speaker alongside neo-Nazis and skinheads, and once starred in a video that compares dark-skinned Caucasus militants to cockroaches. While cockroaches can be killed with a slipper, he says that in the case of humans, “I recommend a pistol.”

Not to mention he voluntarily went back to Russia after believing they tried to have him killed. I don't know what he expected

Also the video of him being racist is still up on his personal YouTube channel to be clear. It is not a position he ever distanced himself from.