Depends on the perspective ...
From a perspective of a developer ,hacker ,ROM flasher-fanatic ..Locked Bootloader is a hindrance .Thats a minority ...
To be precise smartphone were designed to use in corporates and offices .
if I were an employer ,the last thing i would want is ,employees with phones having locked bootloaders ..
As an employer ,I would actually love phones with iron tight bootloaders and encrypted file systems .
Gingerbread introduced Encryption on android and i believe it was implemented on most moto phones rather quickly
That was moto's(and is maybe) target audience .
To put into perceptive
For a locked bootloader + encrypted File system ,it's impossible to extract data from a phone dump without a password and it is relatively hard to get a phone dump .
For a locked BL without encryption (without the option of official unlocking):It still is hard to get a phone dump ,and if there is a patch there is a chance of data corruption to data wipe .Relatively it's still safe ..
For a locked BL with an option to unlock : The dev option wipes the data so there is no chance to recover it .The security level is similar as above IMO .
For an unlocked Bootloader :It will take 10 minutes to dump the data , 5 minutes to copy ...Faster if there is an access to external media ...
The legal definition of computer is
the term “computer” means an electronic, magnetic, optical, electrochemical, or other high speed data processing device performing logical, arithmetic, or storage functions, and includes any data storage facility or communications facility directly related to or operating in conjunction with such device, but such term does not include an automated typewriter or typesetter, a portable hand held calculator, or other similar device;
so a smartphone ,fits the criteria and can be assumed as a computing device .
People have strict restrictions on usage and security of a computing device used for the purpose .
So Locked Bootloader is a measure of protection offered against hacking and data theft to a reasonable extent .
It is more relevant if a data theft occurs and cause damages and it needs to be proved that the relevant device from which the theft occurred had reasonable security in place to prevent such theft .
Thats corporate .Device is not the perspective ,Data is .
For Consumer view ,95% of smartphone consumers dont care enough if bootloader is locked or unlocked or WTF is bootloader .
So it is more relevant to have a phone locked in first place .
Because when you have an option to unlock (the agree button) ,you claim to know the consequences of unlocking which also includes the ability to flash custom kernels or use fastboot protocol to procure data .The responsibility is transferred to you .
If you unlock Bootloader using hacking then it is device tampering to unauthorized access which again is the responsibility of consumer .
If you check the update history of carriers ,OS exploits are patched quickly ,user/UI/device updates take a while ..Again to provide secure system .
Locked BL is a security mechanism which is provided by carrier to avoid law suits related to data theft .