No, arresting former presidents is a bad idea and not in the interest of national unity.
Is your position that former presidents should be completely above the law? If Trump killed his wife, should he not be arrested?
It’s a difficult balance between holding people accountable and not pissing off too many supporters. If Trump were arrested there would almost certainly be civil unrest.
The question is whether public support should even matter. I don't think so. There should be clean investigations and fair trials, no matter whether the suspect or offender is some John Smith from next door or a former POTUS. We're supposed to be a nation of laws, not of men (to quote Jerry Ford).
I understand your position, but the preservation of the union should supersede this. Is Trump guilty of crimes that could send him to prison? Quite possibly. Is it in the nation’s best interest to have him in prison? No. It would just cement existing political divides and normalize Republican calls of imprisoning political opponents for bogus reasons.
Tbh, I'm not fully convinced there will be a "civil war" in the sense. More likely there are local upraises by militia groups, but all of these can be taken care of the police and the National Guards.
Another question is whether a guilty verdict for Trump automatically has to lead to prison. He could also remain under house arrest or some other penalty. Not uncommon for 76+ year olds who aren't a (direct) violent offender.