FIOSETOWN and TIOCSPGRP vs control ttys

[Mouse]

In sys/kern/tty.c, I find

        case FIOSETOWN: {               /* set pgrp of tty */
[...]
                if (tp->t_session != NULL && !isctty(p, tp)) {
                        mutex_exit(proc_lock);
                        return (ENOTTY);
                }

and

        case TIOCSPGRP: {               /* set pgrp of tty */
[...]
                if (!isctty(p, tp)) {
                        mutex_exit(proc_lock);
                        return (ENOTTY);
                }

These are being a problem for me; I want to open up two ttys, neither
being my control tty, and get SIGIO when I/O is possible on either.
Obviously, I can just build a kernel with those tests snipped out;
indeed, I'm doing exactly that to see if my code works then.

But I'm wondering why those checks are there, wondering what hazard I'm
risking by removing them.  Anyone happen to know?

/~\ The ASCII                             Mouse
\ / Ribbon Campaign
 X  Against HTML                mo...@rodents-montreal.org
/ \ Email!           7D C8 61 52 5D E7 2D 39  4E F1 31 3E E8 B3 27 4B