You are mixing several concepts that really aren't related, but, since you did mention a specific example, I will do my best to reply. I have the weekend off as I'm between projects, and the recent PRs have caught my attention. The following response pretermits any discussion of whether the language you cited is actually "bashing", or whether "bashing" has any effect on stock prices, or whether purported "bashing" is even important in the scheme of things, all of which are different subjects.
The example you gave, even though it is not expressly qualified as such, would likely be seen as an expression of opinion by most courts. As such, it would not be actionable at law. However, even if stated as fact and meant as fact, it woud still not likely be seen as defamatory, and, even if it was, the Company would be required to prove actual damage as a result. This is why most companies don't bother with legal action in such instances, and, at most, themselves become involved on message boards in order to "present their case". Any such statements must also be considered in light of their context, as well as other factors that might bear upon the issue.
As a humorous example of "opinion" that actually occurred here in Louisiana many years ago, and I believe is a reported case that I might be able to find with enough effort, a newspaper food columnist wrote a story about a local restaurant under the headline, "Taint cajun, 'taint Southern, 'taint Creole-American....'taint even good" (paraphrased). He then proceeded to absolutely tear the restaurant and its chef apart in no uncertain terms. Yet, after litigation, it was ultimately ruled that the columinist was merely expressing his opinion, and no judgment against him or his newspaper was thus able to be obtained.
In contrast to the above, people may cross the line if the comments they make constitute accusations of specific criminal activity by a company and/or its representatives. Allegations of insiders using their knowledge to trade the company's stock, or of absconding with company funds, and so forth, may well cross that line --- unless, of course, such statements are true, since truth is always an absoute defense. These kinds of statements can be difficult to gauge however, since not all statements that someone has "violated the law" equate with criminal violations of the type that would be defamatory. For example, if I "run a red light", I have "violated the law", but whether such would rise to the level of, or be the type of, ciriminal violation that would valiidly be the suject of purported defamation, is a different inquiry.
Certainly, every scenario must be viewed in light of its specific facts, so it is difficult to generalize, and this explanation is intended only to provide general insight. I'm not making this next remark about you, personally, but sometimes lay people think that all one needs to do is to read a law and then instantly draw a conclusion about a given fact --- I sometimes wish it was that easy, but, in reality, it is best that it can never be so.
In any event, I hope the above has been of some assistance to you. Best wishes.
