They start from the conclusion that Oswald acted alone and work backwards. Circular arguments every time.
Who is this "they" that did this? On whose orders? And who were Oswald's fellow conspirators? Where was his help?
Were "they" the WC, the HSCA, the Church Committee, multiple news organizations, investigative reporters.....? Multiple generations of Americans over half a century. Which one did this? All of them? Now there's a heckuva conspiracy. The idea that you could get all of these disparate groups to come to the same conclusion is...well....I'm not sure how you can think that can pulled off.
This has been looked at/investigated again and again and again and again. All sorts of groups/entities/organizations have investigated it. Did they all start from a lone assassin view and reject contradictory evidence?
Your argument is they didn't find a conspiracy therefore there was a conspiracy to not find a conspiracy. Now
that's circular thinking.
BTW, who were the conspirators that they didn't find? You're vague as to who they were.