My point is really simple actually which is why this extended exchange is so confusing. The question was basically: what are things liberals and libertarians can agree on. I just answered empirically. Look up the opinions of prominent American liberal writers, bloggers, think tanks and wonks on the mortgage interest tax deduction. Look up the opinions of their libertarian counterparts. Look at what economists say about it. There is a ton of agreement!

Basically you discussed law with people who aren't trained to think politically about law but technically about it. Those people might be thoughtful about the technicality but that doesn't mean that they are thoughtful about the politics behind the law.

Your model of DC lawyers is just broken. I don't know what to tell you. They spend probably an order of magnitude more time thinking about the politics of law than they do just learning doctrine.

No, my model of political actors is partly based on people actual political power in Berlin, which is the city I inhabit.

Politicians seem like obviously the wrong place to look for unmotivated, reasoned discourse about policy. The mortgage interest tax deduction, for instance, is very popular because people like getting free money. In the States, people with houses vote at higher rates than renters, tend to make up the narrow slice of undecided voters that determine elections. Moreover, because of framing effects renters don't see it as the tax on renting that it actually is. So American politicians aren't especially motivated to get rid of it even though plenty of them have heard from economists and technocrats that it is bad policy.

I'm unfortunately, not very knowledgeable about German politics (and apologies for the cultural hegemony of American politics) but I suspect German politicians are similarly more concerned with getting elected than promoting good policy (when the two conflict).

Policy debates should not appear one sided. At the moment at which it seems to you that as issue is completely on sided it's likely that you don't understand the actual issues that are at stake.

One place where were are very likely to find low-hanging fruit of one-sided policy proposals is with the very policies it would be hardest to change. This goes for corporate subsidies, popular tax deductions, drug legalization, reform of the prison system etc.

Policy debates should not appear one-sided because if they actually were one sided they would probably have been implemented! It would be the heroic cause of a problem-solving politician. And so the mantra against one-sidedness makes sense for any policy debate in a legislature or an election and most of the policy debates the pit ends of the political spectrum against each other. But there are cases where a policy is not implemented or championed-- not because it has much in the way of two sides, but because there is some other barrier preventing it from being popularized and implemented. I mentioned corporate subsidies in my initial post. They don't poll well. Both sides claim to oppose them. And they're bad policy. They persist because the coalition that benefits from them cares a lot more about them than the coalition that opposes them. So there are votes and financial support for maintaining or increasing them but opposing them won't yield any comparative political benefit.

I suspect there are a number of other one-sided policies that still go unimplemented due, not just to the structure and arrangement of interests but to cognitive biases in the way voters and politicians think about policy. Risk aversion, scope insensitivity, attention span, cognitive sophistication and in particular framing effects are going to make some good policies broadly unpopular with the median voter and cause politicians to shy away. This is the obvious place to look for the low-hanging fruit of a rationalist politics.

Which isn't to say that whole last paragraph isn't a minefield of possible bias blind spots and paternalism.