Idealist sect 582: Let's torture people, in order that we may save their souls.
Idealist sect 230: Let's enslave people, to establish the supremacy of our tribe.
Idealist sect 783: Let's starve people, to show the superiority of our economists.
Realists: Let's do none of that. Instead, let's cautiously improve on things.
Idealists in chorus: You have no Ideals!
Anything can be justified. Many evils cannot exist for long if they are seen for what they are. They NEED idealism to exist. Minimize idealism and everything will be looked at for what it IS, instead of what it might represent in the abstract, that is, what it IS NOT.
The highway to hell is paved with Ideals. Hell, when it is not primal barbarism bereft of any system, is negative cycles of suffering kept on by Idealists. Idealists gloss over evil acts, reiterating their belief that it is all for the common good, that repeated failures do not mean that the Ideal might not one day miraculously work, that the Ideal was hijacked, misinterpreted, applied incorrectly, applied to extremely, not applied enough, etc.
What realists want is perhaps somewhat egoistic, but is in the end reasonable and the right order of things.
What Idealists want is so abhorrent, that they must say they want something very different.
Realists declare and demand their preference. Idealists declare universalism, then use that cover to impose their preference.
Idealists will proclaim with a straight face the truth and justice of an Ideology that has caused immense pain. They will glow with the certainty of absolute faith in a belief structure that has been used to justify inflicting suffering and been used to promote destructive actions, and not for a moment smell the contradiction.
Idealists put all of their eggs in one basket, and DEMAND THAT EVERYONE ELSE put THEIR eggs in the same basket. Then Idealists step into the basket and start stamping in the eggs. If anyone dares utter a word about it, they either say that you can't make an omelet without breaking some eggs, or, that those who object are anti-Idealist and therefor obviously evil.
Realists put their eggs in different baskets, leave some in nests, study some, and trade some. They check every once in a while which of their different choices for a system is doing well (for the time being), and maybe put some more eggs in the baskets that are doing well. They study short term effects and they keep an eye for long term effects. What they do not do is throw eggs at bystanders who point out that maybe one egg has a venomous snake in it.
Realists then have nice fried or boiled eggs, while the Idealists next door are starving. The Idealists then come either begging for eggs, stealing eggs, appealing to Ideals and distribution of (other people's) eggs, trading paper drawings (it's called fiat currency) for eggs, or just using physical violence to get hold of the damned eggs.
Which they then, of course, proceed to put in one basket and trample. Rinse and repeat.
Idealist: we should take guns away from people! Guns are bad! People with guns are evil!
Realist: we have split the country up into regions. The gun-free region has zero guns: the police will use Idealist arguments to deal with gangs, murderers and rapists. Bodyguards will use their cool sunglasses instead of weapons. The army will shout hard at any enemy. Security forces will... well, you get the point.
Many citizens that find adhering to the law challenging, and who are displeased with the police, are just dying to join you Idealists in the new gun-free region. Have fun!