What was Applecheek hoping to gain by locking Tom and Jerry up in the cellar at all? His entire money-making scheme is to kidnap pets from unsuspecting owners and then ask for ransom. His henchmen pretend to be pound employees and Applecheek's "home for neglected furry little creatures" is a good cover for why he has so many cats and dogs around. So far that's a good plan. But since Figg had brought Tom and Jerry fair and square, wasn't there much more to gain by treating them well so he'd get a handsome fee when Figg came back, than by lumping them with the kidnapped pets in the cages? note I am assuming Figg was going to come back for Tom and Jerry later on, or at least assuming that Applecheek assumed this, because if he knew Figg didn't give a damn about them then why wouldn't he just let them go since there was no money to be made off them?
Why is the fact that Tom and Jerry talk (and have musical numbers) such a Berserk Button for the fandom? Yeah, they never held conversations before, but in the theatrical shorts, they talked occasionally and sang all the time. It's not like this was an Ass Pull on the filmmakers' part.
It's probably from association with the film not being very good, or indicative of what Tom & Jerry were about. There's very little of the slapstick that made the original shorts popular, and since the talking and singing take up so much of the movie's time, it isn't unfair to assume that the humour of the source material got stripped out in favor of it. Ergo, the talking and singing are bad because they replaced what made the theatrical shorts appealing to begin with.
Doug and Rob Walker explained it best in their commentary track: "They inherently aren't talking characters. Just because Mr. Bean gives a little speech in a movie, that does not make him a 'talking character'".
Could be the Negative Continuity that the movie implies about the past scenes where they've spoken/sung. The movie makes it clear that neither knew the other could talk, but instead of the few short lines and songs, they talk for the entire movie. Basically, it seems like the movie was disregarding all the old cartoons and treating it like a new gimmick, which pushed away long-time fans.
It's a Misblamed part. The movie very much seems to have thrown Tom and Jerry into a project where two completely new characters may have done better. This is what probably angers most of the T&J public, but the whole "they talk?" thing is overblown by a much smaller but much louder team. The internet no doubt helped that group seem larger than they are, since, after all, if those people had watched more Tom and Jerry over the years, them talking, singing, and being friends are all more Mythology Gag material than insults.