Under the theme of responses saying theism is unnecessary, this one makes a simple claim.
Simple, until one is asked to define "better", and ponder the implications of moral relativism or moral equivalency.
"You don't have to believe in God to make the world a better place."
Of course, the term "better" suggests a value against which something is being judged. Here's where all Christians, at least in principle, have their published universal standard they can all measure against.
Nonbelievers, by contrast, typically reject absolutes and tend to each be more reliant on their own relative judgment. I suppose the ambiguous "general preservation of society" would be the measure of "better" in that case. Just hope the societal measure chosen isn't that of the former Soviet Union, or Stalinist Russia, or Cambodia, or Rwanda, or Uganda, or Sudan, or Syria, or North Korea, or Tajikistan, or Turkmenistan, or Bhutan, or Saudi Arabia, or Somalia, or Mauritania, or Libya, or Maldives, etc.
Some of those states are theistic, others atheistic, but all have terrible records of abuse and repression. Terrible, that is, if there truly exists a universal standard to be measured against.
Is religion necessary to live a virtuous life?
Malice toward none and charity for all?