Question about 3...d3 in Smith-Morra

I find it funny, that advocates of a bad opening love to analyse bad moves (3...d3 +=/=, 3...Nf6 +=/= (alapin main line), 3...d5 +/-), while dxc3 is equal only if white plays with a great accuracy

In my opening book it states in the alapin variation d5 push with exd5 ends whites hopes of constructing an ideal centre

yes 3...Nf6 is equal and comfortable, simply because the alapin is not the best way to meet the sicilian. 3...dxc3 and white struggles to even equalize. it's like the king's gambit, white hopes for 2...Bc5 or 2...d5 but after exf4, white should think about equalizing !! (with white at move 2). it reminds me kosten's book about the latvian gambit. during the 200 first pages, he gives the refutation of all white suboptimal moves, then says why the latvian is refuted in just 1 page