> I can send you 403's just because I don't like your face.
Sure. At least then you're being honest. If you hate me, it doesn't matter what user agent I use to access your site. Browsers, scripts, they are all me.
Why do you think it’s dishonest to send 403s to bots but not browsers? Method of access matters — you the human might have access to your safety deposit box but the bank is still allowed to make rules about your access — like you have to come during business hours and you can’t send someone on your behalf.
I totally can though. If sign a document saying another person can do such and such on my behalf, that person can totally do that. Yes, even at the bank. No different from a user agent, really.