My conviction that Leftism is evil can be explained quite briefly.
Firstly, I define evil as that which opposes the Good; and the origin of Good is God. Thus the root of Leftism is historically, and by primary motivation, opposition to God (specifically, the Christian God - our loving Father and the creator).
(This is why non-Christians are mostly, more-or-less incapable of defining, understanding or recognising evil.)
The way that Leftism operates is to pervert the spiritual into the material. Spiritual 'goods' are made evil by being remade in material form.
An example is the spiritual fact that all men are brothers and sisters; this is perverted into political equality. Another spiritual good is the sexual and creative love of husband and wife - this is reduced into the massively-promoted and enforced materialism that sex = love, love is good, therefore sex is good.
So Leftism is metaphysically evil, because its underlying assumptions are that Life is only-material and restricted to mortality - thereby excluding the divine source of Goodness.
It is literally evil because materialist Leftism is strategically implemented by immortal spiritual beings, demons, fallen angels - and this explains why Leftism can be perceived to have been working to an over-arching plan across many human generations.
So it is not Leftist people or policies that are necessarily evil (and these are almost never totally-evil); it is Leftism itself - the strategy, the plan, the intention and motivations - that is purely, metaphysically and literally evil.