When I was arrested recently I was handcuffed real tight - I didn't give any trouble. When I had court the next day we were all put in cuffs and leg irons too. I was only arrested for DUI. Why do they do this and make you feel like a serious criminal?

Only arrested for DUI! You say You are not a serious criminal. What would you think if someone plowed down someone you loved like your mom or dad or girlfriend and it was their second DUI. Would you think they might be a serious criminal?
It could have happened to you...You did not once but twice arm yourself with a deadly weapon and go out and take the chance of killing people who did nothing wrong but be out on the streets as the same time as you.
And you are talking about being handcuffed and put into leg irons and made to feel like you are a serious criminal! You know what...All the questions you asked tonight are about poor little you. You my friend will go out once again right after you get out this second time and drink and drive. You dont think you have done anything wrong. That is the problem here. I just pray that you open up your EYES before you Murder someone!

Because you are a criminal
Dude, please don't breed

Every jurisdiction has their own guidelines. In some, you're cuffed and shackled like you were, and in others, it's cuffs linked to a chain with several others. It's to make it harder for you to escape.

its called Control, they want to feel like they have 100% control over you in every way they can and all they see is that you are a criminal and every criminal has to be treated the same way no matter what they did. same as they will make you lie on the ground and cuff you if you back chat them the same as if you pulled a gun on them... in their eyes your guilty first and innocent second