May be doubting were easy earlier in history when people were not bombarded by information, ads and products. In our time, doubting is really expensive as it takes a lot of one's precious time in evaluating things and information that one receives and even after a lot of research one can still be in doubt that, if his decisions were right. On other hand, doubting the doubt is even more expensive as not evaluating things may cost both health and pockets. I take a great looking piece of pinkish meat, with no visible fat in it, that is professionally sliced and then put it back, doubting it is healthy. My nose doesn't detect any foul smell, my eyes give it a thumb-up in appearance but my brain doesn't accept these information. These meat are from vaccinated cows and they fatten you. The smell of freshly baked cakes attracts me and then I step back thinking of all those fat and sugar in them. Everything that is bottled, bagged or canned are suspicious. Even water flowing on streams that tickles my soul is doubted for some unknown contamination. These are not the biological doubts (as mentioned earlier senses do not detect something unhealthy) but are cultural doubts that we learn by learning the results of studies. Still these are the minor doubts, healthy and "approved" by the evolutionary-worldview and we can live with it.
The greater issue is however doubting the worldviews out there. As they say, three things, stupidity, language and religion have no boundaries and there are no limits to them. And no worldview is immune of these three things. They are either constructed to support them or oppose them and both in opposition or support, these three things obscure a worldview to unrecognizable level. It is a historic fact that any theology and theory that were adapted by people in power have resulted in burning books, cities and people. From religion to science to socio-economic theories, all have records of doing stupid things. In short, we have learned to doubt the worldviews more seriously than a canned food or piece of nice looking meat in a store. I come again to my "Mr. Positive" (still remember that stupidity and language have no limits ;) that culturally, we are in age of doubts and we learn to keep our doubts, but Mr./Ms. positive advises us that to give things the benefit of doubts (Reasons? that is something to.....)