It is of course possible to answer such a question with pure opinion -- and indeed, many users do just that. But claims like the ones you asked about are analyzed using predictable, objective criteria, and people with a reasonable level of exposure to the law can apply the rules to the facts easily enough.
Can they do so with certainty about the outcome of any given case? No, of course not. But that doesn't mean questions can't be analyzed objectively based on the facts presented:
- A paid B to paint A's house. B painted it the wrong color. Does A has a strong case against B for punitive damages? Objectively, the answer is no in any common-law jurisdiction.
- D made a sign that says "I hope Biden dies." Are the criminal charges against him in U.S. District Court likely to stick? Objectively, the answer is no.
- Doctor got drunk before surgery and amputated Patient's right leg instead of giving her an appendectomy. Does Patient have a strong malpractice case against Doctor? Objectively, the answer is yes.
- A prosecutor secured a conviction against D by lying to a jury about the evidence against him. D has since obtained e-mails in which the prosecutor admits to lying because he found his wife cheated on him with D. Does D have a strong case against the prosecutor for malicious prosecution under Section 1983? Objectively, the answer is no.
- D approached W and offered to sell him cocaine. W agreed to pay $50. After the exchange, W revealed that he was an undercover police officer. D admits to the sale but raises an entrapment defense. Does the state have a strong case? Objectively, the answer is yes.
There is of course room to debate as questions grow more complicated, but that doesn't mean there isn't an objective set of criteria that allow us to reach answers that as objective as in any other SE community.
For instance, Stack Overflow also discourages questions that are "primarily opinion-based". So what happens when someone asks a question that has multiple, equally correct answers because different users prefer different methods of performing the same task? One user's "opinion" is that you should create a .bat file, another user's "opinion" is that using the
move command is more efficient.
Does this mean "How do I move files from the command line?" is an "opinion based" question? No. It has answers that are objectively correct and objectively incorrect, because executing the code either moves the files or doesn't.
Likewise, the question "Is assassinating President Biden legal?" has answers that are objectively correct ("No, because 18 U.S. Code § 1751 prohibits it") and objectively incorrect ("Yes, because Let's Go Brandon").
Undoubtedly, there are users who have no idea how to objectively answer these questions, and they are likely to come up with answers that are objectively incorrect. But that makes the answer bad, not the question.
There is basically no point to this website if the answer these types of questions are off-topic.