Why would white opening with e3 and then f4 be a bad opening?

Getting back to the topic, Stockfish suggests e3 as its fifth choice. Can't be too bad is a mindless computer thinks it's good.

1.e3 is not bad but OP asked about e3 and f4.
1.e3 and f4 is certainly worst than the direct 1.f4 which "prevents" e5(Black can stil play it as a gambit) and allows more flexibility regarding the e-pawn that can move 2 squares in some cases.

@Roper300 If we reduced this topic to just the OP's original question, the vast majority of your answer should be deleted, including the second statement in post #23. Before you judge others, FSU!

Jonesmh ,I am forced to say something a 4 year old retarded kid could understand but obviously not you(not that any of us is surprised).
You are not the one who decides what is useful and what is not. It's the OP.

If you can play 1...e6 and 2...f5 as black, then surely you can play 1 e3 and 2 f4 as white.

@Roper300 Once again, you are off topic. You're showing yourself to be hypocritical. I'm not deciding what's useful, I'm just stating that most of what you said was off topic.

@tpr, 1...e6 and 2...f5 is not the same with 1.e3 and 2.f4.
1...e6 comes as response to 1.d4 or 1.e4 and invites either French or Dutch.
1.e3 is first move and after 1...e5 2.f4 is simply a bad move(white will suffer after 2...exf4 3.exf4 d5).
What remains is to change plans and play an English instead with 2.c4(so no f4) or go for French exchange after 2.d4 exd4 3.exd4 d5(again no f4).
So after 1.e3 e5 we are not talking for the same opening anymore.

After 1 e3 e5, 2 f4 may not be best, but it is playable. 2 c4, 2 d4, 2 a3, 2 b3 may be more appropriate.
Proof of playability:

@jonesmh I found it useful. Even if it was an *exact, 100% direct* answer it was useful because it was like, 'Hey, that doesn't work but you might be interested in this similar thing that does.'

I think one move or two just for one side is not a openning and not bad or good. 1.e3 follow to 2.f4 looks live bird opening, but many others openings includes e3/f4 structure... setups including d4/e3/f4, for example. In this case, e3/f4 depends what black play. Larsen opening include b3/Bg2/e3 and if black play e5 the move f4 is good...