1. Modify C:\Users\<user>\AppData\Local\Bohemia_Interactive\arma3launcher.exe_*\1.*\user.config. Set ShowBeEULA to True.
2. Run arma3launcher.exe -nolauncher -useBE -nosplash -skipIntro and click "Agree"

nosplash and skipIntro are going to be ignored.

3. Run it again with the same parameters (no BE EULA anymore)

nosplash and skipIntro are going to be respected.

People that create external launchers may want to run arma with steam.exe -applaunch 107410 ... (because that ensures steam is running and launches the game with a single command) which in turn calls arma3launcher.exe.
When the launcher ignores additional parameters passed to it, the mods that were requested to be loaded will not be loaded and create a bad experience for the user who will have to re-launch the game (at best) or will be confused and consider that "sh** ain't working!" (at worst).