I think there are some really scary people out there who believe that babies are inherently sinful and need to be "punished", or that all kids are trying to grab control and you need to show them whose boss. I don't want to deny that.
But for me, discipline means teaching and if my discipline is gentle and respectful, I don't see why I can't use it on a baby? Did I yell at him? Never, but that doesn't mean that I didn't say laughingly "Ow, that hurts, don't do that" when he pulled my hair or "No love, don't play with the outlet, it might hurt you" as I lifted him up, hugged him, and carried him back to his dump truck.
Similarly, from an early age I taught him what I did want. For example, I would prefer to be asked for something, rather than being whined at. I'm sure you can relate. So, if he was in high chair fussing and getting impatient while I walked across the kitchen to get him some fruit, I might come back, make a silly face or something to get him to pause his fussing for a moment, and then when I had his attention, guide his little hands through the sign for please, then I'd say "Thank you so much for asking so nicely! Here are some yummy blueberries for you" and kiss him on his little nose. Or whatever. And of course, since at this age they want nothing more than to make you smile, after a couple dozen tries he'd get it and start signing please, or waiting the 6 seconds it took me to get the blueberries.
Of course your baby is exploring, he's like a little scientist trying to figure out the properties of everything he sees or touches or tastes. Of course he has no idea that you don't want him sticking his drool covered fingers in the outlet, or crawling into traffic. But that doesn't mean it's too early to start telling him, gently and respectfully what you want and don't want. If he gets it great, if he doesn't well there was no harm in trying and you can always teach him again tomorrow.