So, should presidents have complete legal immunity?
Absolutely not and that especially must include former (so called) presidents. Even a sitting president can be impeached and tossed on his butt. The republican party had 2 valid tries to do this and we all know how they responded - by trying to impeach a president who has done nothing to deserve it.
Why on on Earth should they?
The whole point of having an elected president instead of a monarch is that they are one of the people with with the same rights and responsibilities as everyone else.
Declare a President above the law and you might as well call him or her a God.
The entire immunity thing going on right now involves Trump and should he have immunity as the GOP claimed he had. They claim "a sitting president" is the one with immunity because if he was drawn into constant lawsuits he would not be able to do his job. On January 6th Trump was in office and the ongoing thing with this is that he was president -- but was he really? Biden had won the election. The powers that be are going to hurdle this to get it over as quick as possible by sending it on to the Supreme Court. Trump and his lawyers want to delay this as long as they can. If it goes on long enough and Trump is elected again you have Trump doing a dance and saying " I'm president and you can't get me! Na na nana na na." (Well, something like that.)
The problem with this quick trial and getting this over seems in Trump's favor because the Supreme Court is now asking Trump how he wants to do this thing. That's the way I get it but this does not sound like justice to me.