And unless you're pure Japanese (genetically speaking), you're going to create a hafu child that will forever be viewed and treated differently by society.
Ain't that the sad truth. After getting out of the McJob rat race in Japan I worked for a while in an academic department that basically prepped advanced kids for semesters/years abroad in upper-level mostly American universities. We had a very high number of mixed (half white) kids trying out for this department, and they applied mostly because they were doing anything they possibly could to get the fuck out of Japan.
Most of them got easy acceptance into the program because their fathers (99% of the time it's the father) spoke English at home so they already had advanced language skills. A few, however...I guess their fathers were those real douchebag types that rock up to Japan with this whole "I'm gonna be part Japanese society!" bullshit and attempt to only speak Japanese at home. Imagine that...growing up hearing either mom babbling in effeminate proper Japanese and then dad speaking this retarded, gramatically-incorrect nonsense with a funny accent. That can't be good for communicative development.
In any event, just about all of them had serious complexes about their ethnic background and instinctively tried to hide the fact that they weren't pure Japanese. Some would pretend they couldn't speak or understand English. This one poor kid, it took me three months of prodding her before I finally confronted her in my office and asked her a question in English, and after a few moments she very quietly, timidly replied, with a perfect British accent, "Yes sir...I understood you." Poor fucking kid, I was glad when we got her a shot at going overseas.
Of course, my halfbreed AMERICAN buddies fucking loved coming to Japan, them being handsome and "exotic" to all the fawning bimbos at the club who would squeal when they could switch from Japanese to English and back to Japanese. Those assholes were walking panty-droppers, and I believe most of them scored different girls just about every Friday and Saturday night they were in town. To them, Japan was like Christmas Day every day, but that's also because they didn't have to grow up in Japan and be treated like a fucking novelty toy item or circus freak every day for twenty years.
To knock up some woman and produce a kid that's going to grow up in a stunted society and be treated like an outcast from day one, and then not even have a father figure around for support, guidance, and at least the language skills it'll take to get the fuck out of there after high school graduation? You're not doing that kid any favors at all.