There was an issue launching Spermination on Macs. A workaround is in place, and now you should be able to play Spermination on Macs again! To read more details, check here:
http://steamcommunity.com/app/363460/discussions/0/451848854984740241/
The more recent problem of launching in the background:
http://steamcommunity.com/app/363460/discussions/0/451848855024868649/
... won't cause the game to not run. If it does start "in the background", simply switch to that window & volia! Enjoy!