It is still not valid … I could have a brilliant religious system and if some brut comes along and forces others to accept it - you blame the brut not the religion … Read carefully what you wrote:
When their belief system was spread by violence
Only when you can substantiate where in the religion it states “we must spread religion using violence” can you criticise it … Where in history was “Islam spread by violence?” The biggest populations of Muslims in any one country is Indonesia … Which missions of Islamic war campaigns went there?