Also another point of the demoncism - if he really would have manipulatively planned to pretend to undergo a dangerous operation just to impress Star, while knowing himself it's not dangerous at all, and plant the info to Pony with the intention of it leaking to Star;
shouldn't he have kept up the act when Star showed up? If he wanted to lure Star to his demoncism to be impressed by the peril he puts himself into, shouldn't he have acted falsely noble and all "no don't try to stop me, it's dangerous, but I want to change and this is the only way" or something?
Instead, he interrupts Star when she's fretting out and tells her not to worry because he's the prince of the underworld, so it's no big deal.
Now, the Tom-bashers are insisting that he lied and manipulated so that he'd get Star to worry over him and think it's dangerous - but when she shows up, worrying, fretting, thinking it's dangerous, impressed and trying to stop him, he immediately tells her he thinks it's just show and that it's gonna be easy for him.
His behavior goes 100% against all this "he was trying to manipulate Star" bullshit. He shoots it down himself and reveals exactly how he thinks it is right away, before the procedure. And then proceeds to childishly argue with Star and piss her off when she pleads with him not to do it because it looks dangerous.
So again, imo people have just decided to hate Tom and are reaching to find anything "proving" that he's a manipulative liar or some shit like that.
Meanwhile Star was given the benefit of the doubt when despite expressing a wish to be a good queen, a great friend etc she kept acting incredibly selfish and irresponsible regardless of the consequences (see Song Day), because hurr durr she's a teenager, she's trying, she never chose to be the next queen, it's hard, her flaws make her interesting and human.
Which is true! But that also makes Tom an interesting, flawed, teenaged character, and not some manipulative lying mastermind.