This thread is full of vague explanations so let me see if I can clear things up a bit.
Firstly: A locked bootloader does not mean no custom roms. I am on a custom rom right now on my locked bootloader Droid X.
A locked bootloader simply means you can't have a custom kernel. This means that the dev community has to base their roms off of the stock kernel for that phone. This greatly limits things that can be achieved. It also increased chances of "bricking" your phone significantly. However tools such as an SBF make this almost impossible, and all it takes it patience to do whatever you would like. All the locked bootloader actually does is slow down the process because devs can (and in my opinion always will) find a workaround. For example the Photon's bootloader encryption has been cracked. And the Droid X has fabulous custom kernels using a very complicated system known as 2nd-Init.
My guess is the majority of those people up in arms about a locked bootloader, probably don't know what it actually hinders. Perhaps they think their phone can't be rooted and must remain stock. This is very far from the truth because as posted above, the Bionic is ALREADY ROOTED.
However, that being said, there is another group of people I assume are up in arms about the locked bootloader and are on the other end of the spectrum. They know every little thing the locked bootloader prevents them from doing and they are either:
1. Convinced it won't be bypassed, and can't stand the thought of a "Blur-based" rom as they have been called as of late.
2. As stated above, find it morally wrong to lock something that is their property, and would rather go with a company that is more involved with the developement community.
At the end of the day, I think the bootloader should be so far down on a list of things to not like about a phone. In a perfect world a locked bootloader would have never existed. But a phone as powerful as the Bionic will be amazing for anyone to use. And in time, there *will* be custom roms for it, and I'm sure they will be great.