According to the BBC,
It is fair enough to say the JW group is extreme, harmful to individuals and harmful to family and social cohesion. It is opposed to modern knowledge, learning, science and some branches of medicine. It teaches an extreme form of fundamentalism and exercises an oppressive control over its members. In most of these ways it is almost as extreme as Exclusive Brethrenism.Russia's Supreme Court has accepted the government's request to designate Jehovah's Witnesses as an outlawed religious group, deeming it to be an extremist organisation.
The justice ministry argued that the group had distributed pamphlets which incited hatred against other groups.
. . .
One pamphlet distributed by the group quoted the novelist Leo Tolstoy as describing the doctrine of the Russian Orthodox Church as superstition and sorcery.
Officials have accused the religion of destroying families, propagating hatred and endangering lives.
So to ban it would seem a good idea, except for one thing: this would erode the longstanding guarantee of religious freedom, and would set a controversial precedent. Who would be next?
See http://www.bbc.co.uk/news/world-europe-39661339 for further details.