Underlying the philosophy of the Left is the unshakeable belief that its goals and motivations are intrinsically and uniquely good, and that all contrary opinions are, by definition, malicious. From this position, leftists can justify any behaviour, however dubious, if it serves their higher cause, and can condemn any action by an opponent, however benign, for being done in the name of wickedness.
Nowhere is it written, of course, that the Left’s beliefs are morally superior. That's simply an article of faith for true believers and, as such, goes completely unexamined. Because people on the Right don't favour the Left's methods, they can't care about the people the Left claims to care about. Period.
In truth, the morality of a political position is irrelevant if has lousy real-world consequences. If wealth redistribution wrecks the economy and ruins people's lives, it doesn't matter that it was well-meaning. Mass immigration might benefit newcomers to this country, but if it harms the interests of the native population, it can't be considered wholly virtuous. Conversely, if capitalism leaves everyone better off than socialism, then it can be considered a good thing, even if it isn't motivated by compassion.
One could argue that a policy is moral if it helps the most needy, even if it screws over everyone else, but that is a subjective opinion, not a foregone conclusion. Often, prioritising the interests of the needy harms them in the long-run as it undermines the people who prop up their existence. Ultimately, morality alone is an unreliable guide to policy and by no means the grounds for claiming that one particular method or ideology is unquestionably right and proper.
If the policies and ambitions of the Left are not universally popular and objectively laudable, it cannot have a monopoly on virtue, in which case its methods must be judged on some criteria other than their intentions. How successful are they at achieving goals that are empirically desirable and generally popular? How much harm do they cause to people's widely-shared interests? And how, in these respects, do they compare with alternative methods?
If state-enforced equality, for example, is a worthwhile aspiration, it's because it delivers the benefits people most care about better than capitalism. Its advocates might consider equality of outcome an innately noble cause, and there may be times of popular support for their position, but it is really just a personal opinion.
It's asinine, then, to claim that opposing the Left's efforts to expand the state and increase public spending is ‘nasty’, since this starts from the unspoken assumption that bigger government is our best and only ethical option, and that all else is, by definition, wrong-headed and uncaring. The absurdity of this thinking should be obvious, yet it's rare to hear conservatives calling out the Left for begging the question and taking for granted the fundamental assumptions on which political differences are based.
This is why most political debate involves people shouting past each other - or, more often, involves conservatives allowing the Left to dictate the terms of the debate, instead of extolling their own position and brushing aside presumptive left-wing dogma.