Conflating socialism and Christianity can create a very blurry and confusing paradigm - especially when each is then compared to Humanism. There are some beautiful concepts in Christianity - love thy neighbor, for example that align well within the Humanist perspective. By saying socialism is similar to Christianity and therefore should alarm humanists is too reductive.
Parts yes, parts no.
Humanism does not reject a perfect future world. That would be unreasonable.
And so far as I know Humanists do not reject idealism. We present a better definition of what is ideal and we leave out the fictions of myth.
Since Humanism is consequentialist, it has no problem with virtue signaling. Caring for the environment. Helping those in need. The consequences of these virtues are compatible with Humanism.