"Here I disagree. Bad information is worse than no information."
I suggest you stop posting then... as all you are doing is spreading bad information.
"Economists are paid to say *something*, so they do. People literally "buy it", then they proceed with their plans."
If they work at a well respected university then no, they're not paid to say anything in particular. This is called scientific freedom. Scientists take it very seriously.
Nonetheless, a portion of scientists are indeed payed by interest groups (such as for instance the pharmaceutical industry, oh wait that's 'hard' science). Such scientists are required to make their affiliations public though. Anyone that reads their publications can take the possible bias into account, scrutinize their methods, search for additional information from independent sources, or derive the information independently themselves. Scientists/sources that are not affiliated with any particular interest group are deemed more reliable.
Such practices are common place in the scientific community because, you know, rather than being defeatist like you, they went and implemented proper procedures to deal with bias. For instance, although the field of Marxian economic theory was initiated by Marx, a wide variety of scientists have since contributed to it. In fact, the entire group of scientists that have contributed to it is so large and diverse that you would have to be an insane conspiracy theorist to believe that it is a biased theory.
"People need to borrow the authority of """""science""""" to have credibility; nonetheless the slippery nature of social science means something suitable is always available."
Sure, you can cherry pick scientific results and this happens all the time in politics. This is a problem with politics though, not with science, because as soon as you start cherry picking with a political agenda it stops being science. This is why you're better off listening to scientists than to politicians if you want reliable information.
"It is for this reason that I think people should have very, very low ambitions for their political and economic agenda."
Yes, that's what you keep repeating. You have however not put forward any explanation as to how "very, very low ambitions" would lead to a better outcome, nor have you put forward any plausible arguments for your premise that social sciences have a "political and economic agenda." As a matter of fact they do not. Political and economic agendas are the domain of politics, whereas the domain of science is the accumulation of reliable knowledge.