You are Both Right. The key is in finding a balance. I tend to have reasoned too much with Alice and so often when I needed her just to obey because we are in a hurry, or I can't get into all the ways because of the audience etc as she got older, she required too much "reasoning with". Here are some things I learned when she was just a little older than yours is now that really helped rebalance us.
Sticking with methods that do not include a reasoning aspect doesn't allow your child to see you model how you think through decisions, ask questions to help them make decisions in the future, or simply understand the rule to apply it later without you needing to step in, but, to keep things balanced, I suggest not engaging in "reasoning" that takes more than a two to three sentences most of the time. If it requires a whole paragraph from you, or is becoming a lot of back and forth, your child is probably not fully grasping all of it any way and may not be ready to understand this particular set of "reasons".
That said, bribing is not a good idea. Convincing because of the good things that are already coming if you child "gets into the car", for example, is different. Never say he or she has a choice if there is no real choice in the matter. Ultimately, you are the boss but you can still explain why you've made the choice you've made (briefly).
I would also personally avoid, "because I said so" and replace it with a variety of things like. "I need you to trust me right now, we'll talk about it later" or "because that is what I need right now". Its really just a style choice, but I find it to be more open to conversation later, than "because I said so - the reasoning part can happen later as they get older".
Lastly, I would suggest that when you can give your child an option, do so. It will empower him/her at times when that is okay so that you can also say, "I let you decide a lot of things - right now, you need to let me decide this one". PLUS it gives your child the opportunity to practice decision making. Look up and Read, "Parenting with Love and Logic" for more information.