One reason is distrust and animosity between the two sides. Although the two parties apparently have stopped doing this, in 2013 at least, colloquies between House leadership members made the depth and scope of bipartisan distrust and animosity crystal clear (the fight begins at about 2:30 of the 44-minute C-Span broadcast). In their dialog, Cantor and Hoyer are talking right past each other. The mutual hate and distrust is obvious. So is the futility of the colloquy, which delivers to the public nothing more than an exercise in partisan posturing. One can presume that the one or both of the parties decided to discontinue engaging in House colloquies like this because the fight makes both sides look intransigent and petty.
Another major factor that adds to the emptiness and deception in two-party political debate is leaving key terms undefined. As discussed before, the human mind subconsciously fills in gaps in knowledge such as definitions. The gaps typically get filled with meanings the mind tends to want to use. even though that can and does lead to errors and misunderstandings, that is just how the human brain works. The process is usually subconscious and it presents a very effective tool for people who want to get a message across. It takes conscious effort and time to be aware of such innate but subconscious activity. It takes even more effort to blunt the impacts of how the human mind can inaccurately perceive facts and process information, leading to flawed conclusions.
Another reason for the dominance of empty debate flows from the adversarial nature of political discourse. In political advocacy, one side argues for policy choices or laws it wants. The advocacy almost always goes on without much regard for opposing arguments or facts that undermine the advocate's argument or logic. In other words, the content is one-sided spin, which is almost always unfair, misleading, grounded in false reality or flawed logic, or some combination of those things. The possibility that adverse impacts to the public interest could flow from one-sided dishonesty rarely or never enters the partisans' mind. The one-sidedness of what advocates tell the public is simply irrelevant to a mind set where all is fair in love and war. Since politics is war, all is fair.
A related factor that feeds the one-sidedness of partisan political speech flows from the the free speech clause of the First Amendment of the U.S. Constitution, which reads: Congress shall make no law abridging the freedom of speech. In the U.S., the scope of protected free speech is broad and the only limits are prohibitions on threats directed to a person or group, child pornography and a few other categories of speech. False statements of fact, which includes libel and slander, are theoretically not protected free speech and are subject to criminal or civil penalty. However, the courts are unsure of how to deal with this and prosecutions are rare and often hard to prove in the realm of politics. The current supreme court trend is on the side of expanding the nature and scope of protected speech in politics. And, since liability for false statements can be significantly limited by simply expressing statements as opinions (honest mistakes) instead of facts, political partisans are largely free to at least deceive and misinform the public, if not outright lie.
Like it or not, that is the sad reality of political speech, not an unsupported opinion. Again, politics is war and all tactics are fair, regardless of adverse impacts on the public interest. The battle is between and among special interests. The public interest is mainly an innocent bystander taking lots of collateral damage hits with a few benefits. Meanwhile the raging elephants fight each other. Partisans on each side would usually agree that this perception of reality applies only to the opposing side. DP takes that as solid evidence that it applies to both sides. In other words, both sides are basically correct when they accuse their opposition of spinning or harming the public interest.
When the scope of free speech is coupled with bipartisan animosity and distrust and the power of ideology and self-interest to distort both reality and logic, reasons to see political speech as mostly empty become easy to see. All of those factors feed into the one-sided nature of political speech and that makes the speech, from the public interest POV, mostly or completely empty and usually more harmful than beneficial.
Unfortunately, spin dominates partisan political debate or argument. Partisans on both sides use it constantly and ruthlessly. Spin can be very hard to spot and one-sides arguments seem more persuasive when no counter arguments are present. That is just one reason why political speech is nearly always one-sided and inaccurate to a significant degree. And, when a person believes strongly in an ideology, that amounts to a powerful but usually subconscious biological force that distorts fact and logic. When that fact, not opinion, is added to the freedom of spin, it is easy to see why political speech is mostly empty and deceptive.
If that bare knuckles attitude applies to political belief about money in politics, why wouldn't the same attitude apply to everything else, including the content of free political speech as viewed from the public interest POV? There are good reasons and logic to support the argument that political free speech is far more empty than meaningful. Of course, that all depends on how one defines things and sees reality, doesn't it?
1. Most partisans are intelligent and fully aware of how to lie, misinform or deceive without running afoul of any laws that punish false statements. Politicians and advocates know exactly where the line is and even cross the line with impunity. Given the court's ideological reluctance to punish political speech of any kind, the risks of expressing lies or misinformation as opinions is nil. It is relevant that many or most democrats believe that republicans or the republican party lie much of the time and the lies involve most topics in politics. Many or most republicans believe the same about democrats or the democratic party. Unbiased fact checking from multiple sources points to partisans often taking liberty with the truth, if not outright lying. Although some must exist, DP is not aware of a single lawsuit and liability arising from any allegedly false statement made by any partisan or candidate for President, Senate or the House in any election since the founding of the Republic.
2. As viewed from a special interest advocate's point of view, spin is better than wonderful. Spin is a powerful tool to get what the advocate wants. Probably the most powerful tool. The importance of always keeping in mind the distinction between the goals of serving the public interest vs. serving special interests cannot be understated.