David Wheeler, whose son, Benjamin, was one of the first graders murdered at the elementary school in 2012, tells TMZ ... Elon's call to let Alex back on the social media app is further proof the guy is a "sociopath."

As you'd expect, he feels the same way about Jones -- who's heinously repeated his theory the Sandy Hook shooting was a hoax -- so, David thinks Musk and Jones deserve each other.

For that reason, he says he's not at all shocked Elon reinstated Jones on the social media platform.

David says he stopped using X/Twitter when Elon took the reins ... and goes on to say Elon and Alex don't care about him, and that's just how they operate in the world.

As we reported, Elon put up a poll on his platform, asking folks whether or not Jones' account should be restored ... and about 70 percent voted in favor of bringing him back.

Jones was given the boot in 2018 while neck-deep in defamation lawsuits from families of the Sandy Hook victims -- which he lost and owes nearly $1 billion to the plaintiffs. At the time, Twitter cited abusive behavior on his account as the reason it was 86'ing him.

Interestingly, about a year ago, Musk -- after buying Twitter -- vowed he would not reinstate Jones because, having lost a child himself, he had "no mercy for anyone who would use the deaths of children for gain, politics or fame."

David tells us the fact Elon reversed field on Jones' X status "based on the opinions of users and not his own convictions, tells me that he has no convictions."