In a Mirror, Darkly (2) - S4-E19
Stupidity: When the Gorn attacks Archer, one of the MACO officers raises his weapon to fire, but fears hitting Archer, so he doesn't shoot. But then he attacks the Gorn with the butt of his weapon. He was close enough to hit him, he could have just stood over him and fired without fear of hitting Archer.
Stupidity: The last remaining Xindi, in desperation, attempts to release the virus over the fan, despite the virus not being fully ready. However, it seems the only reason he didn't release the virus at that time was he had to seek cover from Archer and T'Pol shooting at him and to start shooting back at them. However, he had plenty of cover from the rooftop stairwell, which was right next to the fan, and he had enough time to dump out the contents over the fan.
Answer: While ratings did drop, there was a lot going on to cause the rating drops and cancellation. First, "Enterprise" was on UPN, which was dissolved a year after the show was cancelled. At the time of cancellation, it was UPN's highest rated drama. Because they were on at night, they were often preempted by local UPN broadcast of baseball games. And it wasn't even aired in every market. They also lost a major corporate backer early and it was difficult for them to over come that loss. Plus, for season 4, they switched to a Friday night line up, so they were competing against Fox shows, like "The Simpsons" whereas on Wednesdays they didn't have much competition.
Bishop73