Stargate: 10 Times The Show Made Huge Mistakes
1. WHY. DON'T. THEY. KILL. IT?
In season five, SG-1 makes a very startling discovery. They find an android, who later reveals her name as Reece, lying alone on an empty planet. That is to say, the planet is mostly empty, except for a large amount of Replicator blocks. This is the first example of Replicators in the Milky Way galaxy - huge, disastrous news for all concerned.
First issue: they do not immediately contact the Asgard. Hmm.
When Reece is activated back on Earth, she is quickly revealed as a child-like personality, albeit one with immense strength. She gets into an altercation with Daniel Jackson, after which she shows him her 'toy'.
The Replcator that then crawls out and onto her arm quite deservedly causes extreme alarm in the SGC. They trap it.
Repeat: this herald of death is kept in a cage, rather than destroying it.
It is an enormous plot hole, mostly due to the fact that it had been repeatedly shown that trapping a Replicator is as safe as moonwalking backward through a destination Stargate.
Fun fact: there is yet another swipe card mistake in this episode! Someone really should have explained swipe cards to the production team!