I don't know their answer, but from my point of view, enlightened only by reading crime fiction books, there may be many scenarios where a throw down gun may help the good guys.
For example, you chase two suspects. One stops, produces a gun and points it at you. You react fast, just as trained - you shoot and you drop the bad guy. The other suspect grabs the gun and runs away or, as an alternative, throws it into a bottomless pit - which may be a river, or a big truck going by, or a train, or some other convenient means of disposal. Long story cut short, the gun will never be located. You may fish it out of the river, but the fingerprints will be long gone.
This is not contrived - bad guys do not want to be caught with a weapon, especially with a "hot" one. They want to dispose of it. If they are successful you are left with a slowly cooling body that has no weapon on it. Any court will review the evidence and say that you shot an unarmed guy. Dura lex sed lex, as they used to say in Rome.
The opposition is not always playing by the rules. As matter of fact, it never plays by the rules. They will want to hurt the cop at every opportunity; a setup is not just possible, it is very likely. If the cop wants to escape the trap he has to bend the rules in the other direction, to make things fair again. In the end a crooked cop will be doing bad things and an honest cop will be doing good things. The presence of a throw down gun will not prompt a good cop to shoot people left and right. The bad cop will not need a throw down gun - he already has you framed in a much better, carefully planned way. He will stuff your car and your pockets with drugs, cuff you, and you will spend the next 20 years of your life in confinement. The cop's actions will not be even questioned. If he is so desperate to kill you he will inject you with an overdose. Who is going to investigate that, and how?
No, you are wrong. Both legally and morally: first the telling of lies under oath is perjury; second, the Bible clearly says “You must not testify falsely against your neighbor.” [Exodus 20:16, NLT].
If some crime must have the prosecution resort to lying to secure the conviction, then regardless of the actual-guilt of the accused the accused ought to have been acquitted. -- That is the introduction of lies on part of the prosecution is, in itself, reason to cause a reasonable doubt.