Which means you should have sound reasoning behind your position. And you should be able to explain your reasoning to somebody else. If you can't really explain your reasoning, it's likely that you did not think everything through--and if you did not think everything through, being an expert does not mean you're right!
I think of this just in terms of myself. If I hold a position but I can't explain it, it means I need to rethink it. If I've put some thought into a position--which is my goal for everything important--then explaining myself is just a matter of voicing my existing rationale.
So I think you should never be offended at having to explain something: at the very least, it's a way to clarify your own thinking and highlight assumptions. And if you're making good decisions anyway, it's easy!
There are times when, to be blunt, you (hypothetical you) don't have the background for me to explain my reasoning - and certainly not in the timeframe of a conversation when I need to catch you up on potentially decades worth of research. It is possible, especially if you're not willing to either take some things as given, that you are not qualified to understand my reasoning.
Because you are not an expert
And that's fine. There are things about which I am not an expert, to which the same principles apply. Computer science among them. Along with particle physics, Russian literature and modern cars.
Taken in sufficient context, I think your point is a good one. But I get the sense that this is not the main thing bugging the author; what seems to be bugging him is that he is under pressure to justify his positions to a broader audience than would have existed in the past, and he may be having a hard time doing that.
If he's making a point during a conversation with other experts about the cumulative costs in litigation of a certain policy implemented in some state in 1979, he's the boss. But if he's making a broad point about the welfare state, he's got a larger group of (well-informed) interlocutors to deal with and convince. I suspect he wants his expertise to carry weight on these larger questions as well.
Which means you should have sound reasoning behind your position. And you should be able to explain your reasoning to somebody else. If you can't really explain your reasoning, it's likely that you did not think everything through--and if you did not think everything through, being an expert does not mean you're right!
I think of this just in terms of myself. If I hold a position but I can't explain it, it means I need to rethink it. If I've put some thought into a position--which is my goal for everything important--then explaining myself is just a matter of voicing my existing rationale.
So I think you should never be offended at having to explain something: at the very least, it's a way to clarify your own thinking and highlight assumptions. And if you're making good decisions anyway, it's easy!