That's not justification; that's you admitting you don't have any justification
Seriously, think about why you believe what you do. If you can't see any reason to believe it, it's irrational to believe it by the definition of rationality!
Well I'm not sure, unfortunately I don't have many answers. However, I think an ideal justice system would focus very much on the suffering of the population it manages. 'Retributive justice' (i.e. causing suffering to criminals for its own sake) would not feature, since it increases the net suffering for no consistent reason. Instead, important factors would be how we can protect the public from truly dangerous criminals, and how (or if) we can get other criminals to well, stop being criminals!
I think I've provided some level of justification, but how far back should we go? We have to start somewhere, otherwise we'd end up in an infinite loop where the premises of every justification are hit with another request for justification. And so on.
Do I have to? I responded to your post in particular because I got a notification from that page and thought what you said was interesting. I haven't read this whole thread, and I don't intend to - I wouldn't get anything else done!
If you don't want to have a discussion that is 100% okay and no one will judge you for it (or I won't, at least). But I don't think it's reasonable to make out that the people questioning you on your position are somehow being rude or unfair for doing so.
I don't know who said that but it doesn't sound very constructive, no!