I really don't think it's clear cut. There are certainly aspects of the religion that are harmful and have damaged people and led to the people dying, specifically shunning, protection of the organisation's name over protection of the person, blood transfusions. I fully sympathise with every victim of these serious and morally reprehensible actions and would never wish to minimise the impact that every case of this has had on those concerned.
It is true that these are harmful aspects of the religion, and can easily be framed as extreme beliefs, but the social exclusion, passive aggressive behaviour and holding a belief that you are prepared to die for are hardly unique to Jehovah's Witnesses. Are they extreme in the sense of wanting to secure their agenda through violent actions? No, even if you accept that their view of Bible does promote God doing just that.
On a day to day basis Witness pose no threat to their neighbours. It's the relative minority of cases where families are caustically split through shunning and even more of a minority that have seen a relative die as a direct result of the blood policy. In wider society, family upset and discord affects many, many people and people follow all sorts of behaviour that is harmful to themselves and their kids (e.g. smoking, obesity). Again, I don't wish to minimise the harm but just try and contextualise it.
The problem with the way this has been spun in Russia is that it is all part of a wider agenda that the government has to recreate the oppressive culture that was a hallmark of the days of communism. When the same arguments are used to oppress gay people, other religious minorities and those who speak out against Putin then I find it really difficult to find much to be pleased about with this ban.
Of course it's great that the WTS is being dealt a blow but did being banned in the past prevent people from joining? No. The WTS is unlikely to decline through the suppression of it's activities but can be undermined through education. The more people are educated into not accepting religious dogma, researching their beliefs and able to access resources that give them the whole story then the less hold the WTS society will have on their minds.
So I don't have an argument in principle with the view that the WTS is extreme but consider this to be relative. I don't support the abuse of Russian law to undermine freedom of speech but I would happily support the WTS being pulled up over it's tax free status and it's lack of a progressive child protection policy for example.