Check your history of QBs. The only reason you throw them in the fire is when you have no other option. The Rams have other options...they are Keenum and Foles.
Rather than argue the point realize no one made the move to take Foles from the Rams, so I think this is the depth chart at QB opening day:
1.Keenum
2. Foles
3. Goff
I know my history quite well. And I don't consider Foles or Keenum to be options you sit a #1 overall QB for. But here's a list of QBs thrown into the fire since Peyton Manning was drafted who had successful careers:
Peyton Manning
Russell Wilson
Matt Ryan
Joe Flacco
Ben Roethlisberger
Cam Newton
Teddy Bridgewater (so far)
Jameis Winston (so far)
Marcus Mariota (so far)
Andrew Luck
Andy Dalton
Derek Carr (so far)
Blake Bortles (so far)
Ryan Tannehill
That's a list with a lot of successful QBs on it. You'll also notice that most of the young QBs are on it. Because teams aren't sitting QBs anymore.
All of these teams had bad options that they could have stuck with but they felt that starting their rookie QB was the better move and that their rookie QB was ready. Bortles is the only one out of this group who I really felt they were wrong about. But it didn't ruin his career.
And when you look at this list, guys like Flacco, Roethlisberger, Ryan, Wilson, Luck, and Dalton got their teams to the playoffs as rookies.(RGIII did too but he hasn't had a successful career...for other reasons)