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

I've played it in a few games and they turned out okay but it doesn't seem to be a studied opening and the computer doesn't think it's very good. What would be the reasons for white not to open with e3 then f4?

you completely destroy your kingside, meaning your opponent can easily get an attack in. At 1300 i guess it's "working"

At the beginning of a game, the f2 square is the weakest - only defendable by the king. As such, it is the target of many traps and attacks. Also notice how the diagonal on the king side can't be defended by the knight or bishop. Keep experimenting with that opening against better players and the vulnerabilities will be more apparent.

It's a dubious opening in that it is very easy for Black to equalize White's initial advantage or even gain a slight advantage. I mean, any opening is playable if you are sufficiently strong compared to your opponent, but playing e3 e5 f4 exf4 puts you at -1 and the game has basically just started. Against an opponent of similar rating to your own, that should result in a win for them more often than not.

If you want to play this kind of line, it looks like playing f4 immediately (Bird opening) is a better move order even if you end up in the same position (typically Bird is something like f4 Nc3, e3 for White) because you discourage your opponent from playing e5. Bird opening is still a bit dubious, but it's relatively popular and White has decent chances with it.

Hey Roper300, would you be so kind and tell me how you managed to paste the interaktive Chessboard into the forum?
Thx... a newbie.

e4e5f4exf4nicht, you make a study and then you copy and paste the URL of the chapter from the "share & export" option. I just recently learned it myself thanks to Skittle-Head.

I think the problem lies with space and the potentially backward d or e pawn.
When you advance f4 then you are kind of relying on the e3 pawn to cover the a7-g1 diagonal. This fixes d2 and e3 in the short term, and white would not want to push their queenside pawns immediately since d2 or e3 could become backward. This means black could potentially look to gain a boatload of space on the queenside, which we know engines love a lot. As black's queenside pawns continue to advance, eventually white either needs to either accept backward center pawns or get squeezed. I guess this is why the engine doesn't like this opening too much.

With every move you make you want to get the most out of it, with e3 and f4 you aren't really creating any weaknesses but you aren't making your pieces much more active, so you will be giving your opponent the ability to control the game unless they respond in a similarly lame fashion