Amarande: Alternatives are dangerous for Black. Here is a natural one (which is apparently the second most popular move, despite its hazards).
1 e4 e5 2 f4 exf4 3 Nf3 d6 4 Bc4 g5?
<Not sure this is really losing but it's playing with fire for sure. Play h6 first!>
<Time for a walk on the wild side>
5 ... g4 6 Ng5!
<An improved vein of Allgaier! And as with other f7 based attacks it seems only a tiny little bit is needed to put Black in serious peril, viz. most Fegatello type variations where White gets even one extra useful move before Nxf7>
6 ... Nh6
<He could return the pawn with Be6, but his position would remain badly inferior. This is the only way to defend f7. Now White's Knight is trapped as in the Allgaier, and will be caught by f6 unless he plays 7 e5; but under the circumstances this would be such a pusillanimous move>
7 d4!! f6
<I don't think Black can really afford this. The King's side is broken up and too few pieces are active. At the least, White's play is at least as sound as any other N-sac KG opening line I can think of>
8 Bxf4 fxg5 9 Bxg5 Qd7
<Misfortune already! That Bishop never does get developed, but if 9 ... Be7 then 10 Bxh6 and Black is a pawn down and exposed to attack without compensation>
10 O-O Nc6 11 Nc3!
<Quiet moves while a piece down are the right policy. Black's material advantage is suppressed as long as he cannot develop his QB and QR; such overt attempts as 11 d5 or 11 Bxh6 Bxh6 12 Bf7+ and 13 d5 simply let Black's Knight get into a happy place>
11 ... Bg7 12 Nd5! Nf7
<In order to castle, for which both White's KR and KB must be shut off. Bait is 12 ... Bxd4? 13 Qxd4! Nxd4 14 Nf6+, and due to the sweeping diagonals of the White Bishops Black not only loses back the Queen forthwith but too many of his loose men go lost shortly as well.>
<A mirage would be 13 Rxf7 as although White does win the Queen by force, Black now gets too much of a ROI on it>
13 ... Bxf6 14 Bxf6 O-O?
<This was Black's plan but may be the losing move! After Rg8 Black seems to have more tenacious prospects?>
<Threatening Qg5#, and if h6, then equally Qxh6! and wins due to the pins>
15 ... d5
<I now played 16 exd5, which is far inferior and allowed Black to hold out longer. 16 Bxd5 appears to lead bluntly to an immediate decision, as it looks that Black will not be able to find an alternative to Qxd5 remaining with two pieces for the Queen. The game continuation is shown here, with all the romantic King's Gambit verve.>
<Threatening 17 d6 with similar effect to the above note>
16 ... Na5
<In order to answer 17 d6 with Nxc4>
17 Bd3 Qxd5 18 Rae1! Nc6
<The threat was 19 Re5 with apocalypse, as Nxe5 allows Qg5+ and mate in two more moves, while a Queen's move would allow Rg5+ and much the same denouement>
19 c4 Qd6 20 Qc2!!
<A calm shift that is immediately decisive! I don't feel bad for missing Bxd5 at this point. The threat of Bxh7# cannot be covered satisfactorily>
20 ... Ng5
<An abject pleading for mercy. If Nh6 or Nd8, then 21 Bxh7+ Kf7 22 Qg6#; if Nh8 then 21 Bxh7+ Kf7 22 Bxh8+ leads to mate; if Re8 21 Bxh7+ Kf8 22 Qg6 and Black cannot meet the threats to his King>
21 fxg5 Ne7
<Mate by Bxh7 and Qg6 was still on the table. Black's position is hopeless, and he will have to give up even more material, after which he will still succumb to mate>
22 Rxe7 Qxe7 23 Bxe7 Rf7 24 Bxh7+! Rxh7 25 Qg6+ 1-0