Physics must be open, critical and responsive […] Physics, good physics, is conflict. Nancy Cartwright
Doubt is not a pleasant condition, but certainty is absurd. Voltaire
In theory there are lots of discussions going on in physics. You can ask questions after a talk, or you can email the author of any paper. In practice this is certainly not enough and doesn't work well.
Even if one is brave enough to ask a somewhat critical question, it is really easy for an experienced speaker to ignore the question, talk for 5 minutes about something unrelated until everyone has forgotten the question. Moreover, most authors do not have the time to answer questions to their papers, because they have to publish new papers. In addition, if someone finds some error in a paper this means nothing but trouble for the author and zero reward. Hence, if a student finds something unclear or stumbles upon an error, he has almost no way of reporting or discussing it.
Therefore, a huge step forward would be if comments would be allowed below arxiv preprints. This way, authors would only need to answer questions once, get more feedback about what parts are unclear and, in addition, readers could help each other.
This would also help to display how people really think about given papers, because nowadays comments on theories or models are really rare, because they have to appear as a fully polished paper.
I disagree with you that this is a discussion that should only be held privately to protect funding. What has actually been happening over the past decade or so is that as the problems with string theory and SUSY have become more apparent, the refusal to publicly admit this, and the choice to start adopting multiverse pseudo-science instead, has damaged the interest of HEP theorists immensely. Look at it this way, if you’re a non-HEP physicist trying to decide whether to hire in HEP theory, having HEP theorists saying that past ideas haven’t worked out, but they’re moving on and trying to find new ones is not a strong case to hire them, but it’s something. If instead you’re being asked to hire people who refuse to admit that what they’ve been working on doesn’t work, you’ve got a very strong case not to hire them. I think Turok has it right: make lemonade.