For real. They're in war, it would be crazy not to use dragons if you could. She caught them in an open field so only soldiers went down. She basically listened to Jon and others about not going straight up to the Red Keep and burning the whole city. I don't see anything wrong with what she did. Her back was up against the wall when 2 of her biggest allies were taken out and the Unsullied were boxed in at Casterly Rock. She did what she needed to do to even the score
You have to think of it as it applies today. Her having dragons is like having a nuke. No one else has a nuke. It's a hard angle to sell to the people. "I have these dragons, but they will never be used on you, on your land." It's hard to spin that in a positive light...remember no matter what, she's still burned the soldiers from the country she plans to rule over. Even though the open field was fair game, it'll come back like "she used those dragons to burn your countrymen, your husbands, brothers and sons. She didn't even fight fair in the war. She will use the dragons to burn you." Tyrion was advising her for the long game...to win the people over.
That's also why he need the Tyrells. Can't come into a country with savages, dragons and a slave army and expect the people to love you. You need names they recognize.