There actually was a batch transfer originally, the problem is some people went a little crazy with it (I'm not sure if it was intentional or accidental). Where it was "too easy" to make 500 or 1,000 (or more) with a single click and then the clean up process of that mistake was more trouble than the bulk create mode was worth. As a bit of a compromise, the overlay was made to work as a non-overlay if you want and then you can just hit back/submit a bunch of times. For example, if you right click the transfer button and open it in a new window, you will get it as a normal page (rather than an overlay on an existing page). At that point you can just submit it as many times as you want.
That being said, I'm not opposed to bringing back the bulk mode, but it would need some sort of confirmation/protection so users aren't doing it inadvertently and then spending more time than it saved going through and deleting those logs one by one.
As far as the public vs. private thing, have kind of gone back and forth on that in the past. The default middle-ground of Shared (viewer must be logged into an account here) is actually pretty private for all intensive purposes unless you choose to share it with someone who's a user here. The URL is never published anywhere, so you would have to go out of your way to share it with someone. That also protects it from inadvertent sharing (public allows anyone to view it even if they aren't logged in here so it doesn't get picked up by a spider or something [Googlebot isn't going to log into an account here]). It's along the lines of something like a cryptocurrency key... it's not password protected or anything, but it's pretty well protected simply because of how many possibilities there are. At it's core a Bitcoin private key is a random 256-bit number, if you guess the right number, you could empty that wallet. But the amount of possibilities in a 256 bit number is 2 to the power of 256, which is 115,792,089,237,316,195,423,570,985,008,687,907,853,269,984,665,640,564,039,457,584,007,913,129,639,935 possibilities. Now the log IDs have 64 possibilities per character (a-z = 26, A-Z = 26, 0-9 = 10 and then also - and _ can be used... so 64 total options) and 8 total characters. Which makes the number of possibilities for someone to randomly guess is 64 to the power of 8. Not as many as Bitcoin, but it's a high enough number that no one could guess it randomly (and certainly not a user that was logged into an account here... the server would shut them down real quick if they were trying to brute-force/guess). Specifically 64 to the power of 8 is 281,474,976,710,656. So it's a 1 in 281 trillion chance someone could randomly find one (and they would need to be logged in and they would be banned as a user automatically after about 15 failed tries). Just like someone could extract all the funds from your Bitcoin wallet if they guess the right number or someone could decrypt an SSL connection if they guessed the right number, there are just too many possibilities to make it actually possible.