Since the FUD Agents do not operate alone, but with support from one or two other user group members, it is better to call them the Sick FUD Units [SFU's*] and their simple mission appears to be to confuse, rant and spam promoting their principal.
SFUs irk and irritate because, they abuse free software to promote non-free software. The SFUs very conveniently use free software to promote themselves, but ask others to go away and try something else. SFU spam [shit posted as mail] is a dead give away and the vigilance of the majority is the only check against FUD operations.
Abraham Lincon said "Most governments have been based, practically, on the denial of equal rights of men ... ours began, by affirming those rights ... We made the experiment; and the fruit is before us. Look at it - think of it."
Non-free software essentially denies equal rights of men to know and use software. Free software gives this right and freedom. There are no keyboard shortcuts to understanding this truth, and one has to think, the way Lincon eloquently spoke during a troubled time in the past. HTH.
*SFUs mentioned here sound functionally and confusingly similar to Windows Services For Unix, SFU, also from Microsoft. Both are sub systems for interoperability, but one targets machines and the other targets people :)