You are right in as much as God is our sole judge, but do not forget He has sent His Guidance for Mankind in the form of His Book. Anybody who does not follow His Commandments or rejects them, has gone astray. While we are neither required, nor even encouraged to force anybody into following The Quran, we certainly can differentiate between those who have chosen to believe and those preferring to go astray.
We, who have chosen to believe, have decided to uphold His Beacon; to give hope to those who lost their way by lighting up their darkness, and help them find their way towards the clear and evident truth. We believe He alone is the Fountainhead of all knowledge, and our only means of getting direct guidance from Him is through His Criterion, The Glorious Quran!
The major part of our mission is to incorporate Allah's commands as accurately as possible in our own lives. This is what we try to do on this forum most of the time.
I end with this prayer in utmost humility: “Our Lord! Take us not to task if we forget or miss the mark! Our Lord! Protect us from placing extra burden on us as those before us caused to be placed on them. Our Lord! Impose not on us anything beyond our strength. (And if we falter) pardon us, absolve our faults, and bestow Grace upon us. You are our Supreme Master, so help us prevail over the community of deniers.” (2:286)