“love thy neighbor”, to me this kind of moral injuction is a form of social coercition, and therefore opposes to the humanist core value of autonomy.
(1) People should be free to act with virtue, otherwise the concept of being virtuous is irrelevant (a quote from Milton Friedman).
(2) You care for yourself, for your family, and your fellows. This is in your own personal interest too. Parents who don’t take care of their children, will likely not be taken care of by their children when they will be old (especially in open western societies where people have the choice to do so). People who are nasty with others will likely be treated badly in return one day or the other. Same for the environment, btw. (Talked about it here)
(3) From (2), we can see that acknowledging the dark, but real, aspect of human nature (selfishness) leads, from a consequentialist point of view, to more, not less, ethical consequences. Because it enhances human welfare, which is the highest good. On the other hand, imposing moral injunctions does not make humans more moral (less selfish for example). This has been tried for thousand of years and never worked (women suffered from prejudices, homosexuals were killed, children were exploited, lands were conquered with no reason but territorial gains, etc.).
By “idealism”, in this brief synthesis of the historical relation between socialism and Christianism/idealism, I referred mainly to the meaning of “metaphysical perspectives asserting that, most fundamentally, reality is equivalent to mind, spirit, or consciousness; that reality is entirely a mental construct; or that ideas are the highest form of reality or have the greatest claim to being considered “real”.” (Wikipedia).
I do agree that as humanists, we do not need to reject full-blown a certain form of idealism in the ordinary sense (“the cherishing or pursuit of high or noble principles, purposes, goals, etc”, Collins dictionary).
What I would retain in this “idealism”, is the word “goal”.
We indeed do need to set goals, if anything has to be achieved.
I think many philosophical and artistic movements (European romanticism, philosophical idealism, post-structuralism, existentialism, etc.) are nihilist[1] in the sense that they are radically pessimistic about the capacity of human beings to achieve (a) any form of objective knowledge of reality and/or (b) any form of happiness. And by being nihilist, they prevent humans to set goals, and therefore lead to failure, and therefore their nihilist prophecy will come true as a self-fulfilling prophecy (and they will be able to say they were the most brilliant and deep forecasting minds then 
).
Consequentialism, in philosophy, is “simply the view that normative properties depend only on consequences.” (SEP).
It stands in opposition to virtue ethics.
Consequentialism is incompatible with virtues.
[1] “a viewpoint that traditional values and beliefs are unfounded and that existence is senseless and useless” (Merriam-Webster)