In case there's more than one interpretation let me define infinity threading.
A Technomage wants to thread. By rule, he rolls dice: hits become rating increase. He does not have to take all of the hits showing, thus he could theoretically take zero hits. The fading test is made against hits -- no hits, no fading. Then in the FAQ, threading does not require an action. "Threading does not require an action; any Fading damage taken applies before the technomancer’s next action (or before they thread anything else)." This is because the technomancer is supposed to be able to thread two or three or more CFs if needed for the upcoming action. (example: thread command, thread gunnery skillsoft for biowire).
This can be tedious for everyone at the table when the TM is trying to get a maximum size thread.
Infinity threading, then, is allowing the TM to declare his target and roll fade against the necessary number of hits. It's obviously more convenient for everyone at the table, and again there's no damage missed when the fading target is zero.
The rebuttal is in one word: glitches.
There are two opportunities for glitches: while threading, and during the fading test. The more times the TM rolls, the more chances for a glitch, or a critical glitch.
Skipping the chance of a glitch is skipping the chance to let your GM's imagination play. After all, what possible "oops" can come of a threading glitch? (Two words: brain fart. more formally, mental paralysis. you just can't thread that cf. Maybe any CF. for how long? Count the ones and cue the evil laughter.)
