“Most people who are OTD are otherwise decent human beings. “
This is very debatable. There are many who go OTD that are very far from decent human beings. And there are many of the YCT persuasion that are evil nasty people who specifically seek to harm frum people.
“Not keeping Shabbos is not an indicator that one would be a murderer, Thief etc”
If your only definition of murder is stabbing someone in an alley or shooting someone with a gun perhaps not. But what about ????? as defined in ???? which would include pulling the plug on an ill patient who is still alive according to ???? or withholding nutrition from a patient on machines. That is ?????. And it an absolute surety that someone who does not keep Shabbos is very likely to be involved in ?????. And they are more likely to condone abortion as a choice and they are likely to ignore halachik definitions of ownership and be involved in ????? ?????. For instance if they gamble amongst each other in cases where you would not say there is an ??????.
Your supposition is utterly wrong.