I am trying to launch Settings through adb using the adb monkey command, but it keeps printing out "Killed". How can I find out what is causing this?

adb shell am start -a android.settings.SETTINGS

To bring up developer settings (in Gingerbread at least):

adb shell am start -a com.android.settings.APPLICATION_DEVELOPMENT_SETTINGS

Here is a bash script to demonstrate more settings - on my Nexus One, it crashes and reboots a few times...

#!/bin/bash

# This FC's android

#      android.settings.WIMAX_SETTINGS:

# list of commands were commied from output of this:
# adb shell dumpsys | grep "SETTINGS"
# quick hask that seemed to work, but prob. not correct.

while read L; do
  [[ -z "$L" ]] && continue
  printf "\nTry [%s]\n" "$L"
  adb shell am start -a ${L:: -1}  # remove trailing colon
  sleep 5
  printf "NOTE: Watch screen... Settings may FC and after a few seconds android will reboot\n"
  adb wait-for-device
done <<EOF
      android.settings.DATE_SETTINGS:
      com.android.settings.APPLICATION_DEVELOPMENT_SETTINGS:
      android.settings.LOCATION_SOURCE_SETTINGS:
      android.settings.MEMORY_CARD_SETTINGS:
      android.settings.LOCALE_SETTINGS:
      android.search.action.SEARCH_SETTINGS:
      android.net.vpn.SETTINGS:
      ACCESSIBILITY_FEEDBACK_SETTINGS:
      android.settings.ACCOUNT_SYNC_SETTINGS:
      com.android.settings.DISPLAY_SETTINGS:
      android.settings.INPUT_METHOD_SETTINGS:
      android.settings.SOUND_SETTINGS:
      android.settings.WIFI_SETTINGS:
      android.settings.APPLICATION_SETTINGS:
      com.android.settings.SOUND_SETTINGS:
      android.settings.ACCOUNT_SYNC_SETTINGS_ADD_ACCOUNT:
      android.settings.MANAGE_APPLICATIONS_SETTINGS:
      android.settings.SYNC_SETTINGS:
      android.settings.SETTINGS:
      com.android.settings.DOCK_SETTINGS:
      android.settings.ADD_ACCOUNT_SETTINGS:
      android.settings.SECURITY_SETTINGS:
      android.settings.DEVICE_INFO_SETTINGS:
      android.settings.WIRELESS_SETTINGS:
      android.settings.DISPLAY_SETTINGS:
      android.settings.SYSTEM_UPDATE_SETTINGS:
      android.settings.MANAGE_ALL_APPLICATIONS_SETTINGS:
      android.settings.DATA_ROAMING_SETTINGS:
      android.settings.APN_SETTINGS:
      android.settings.USER_DICTIONARY_SETTINGS:
      com.android.settings.VOICE_INPUT_OUTPUT_SETTINGS:
      com.android.settings.TTS_SETTINGS:
      android.settings.WIFI_IP_SETTINGS:
      android.search.action.WEB_SEARCH_SETTINGS:
      android.settings.BLUETOOTH_SETTINGS:
      android.settings.AIRPLANE_MODE_SETTINGS:
      android.settings.INTERNAL_STORAGE_SETTINGS:
      android.settings.ACCESSIBILITY_SETTINGS:
      com.android.settings.QUICK_LAUNCH_SETTINGS:
      android.settings.PRIVACY_SETTINGS:
EOF

Since the question is about launching the Settings, there will also be some people looking for the adb command to kill the Settings.

Here you are:

adb shell am force-stop com.android.settings