"Why don't you kill the Green Goblin?" doesn't get thrown at Spider-Man all that often. And even when it does, the writers are usually on his side. I don't know where you're getting this idea that every person who writes the Punisher is on his side and tears down other heroes to prop him up. If anything the opposite happens way more often.
It gets thrown at him and other heroes often enough, and the cliche 'prison is just a vacation because they break out effortlessly'.
Both problems are purely the creation of the medium. 90% of the time, the justice system keeps those who are arrested from breaking out, yet it's still used to ding the hero community. Hell, there was even an Avengers crossover about it.
But Castle?
He's got an ideological shield stronger than steel. DD and Spidey will denounce him as 'killing solves nothing', but what story has been built upon it? His victims are the worst people, as are anyone who wants revenge for his killings, the cops hunting him are lucky to be treated as serious as Daffy Duck and his methods never fail, even though you'd think it would be hard to have CIs when you slaughter every criminal you cross.
In his own book, Castle really does punk a lot of superheroes. DD, Spider-Man, Wolverine...That said, this happens to Frank when he appears in other hero's books as well. Almost as if this is a staple of superhero comics...
Keep in mind that you have about as much chance of changing my mind as I do of changing yours.
So the question is, is the Punisher someone who would have gone after someone like Kyle Rittenhouse before the verdict was given? Or is he Kyle Rittenhouse?
The spider is always on the hunt.
Yeah, he's stated outright that he's not a fan of the majority of mainstream superheroes beyond Superman and a handful others. The Boys and The Pro are vulgar satires of the genre. Afterwards he kept doing comics, but most of them ( outside of the occasional Punisher mini ) are war or espionage oriented.
It's not just Garth Ennis, though he is the worst offender.
I can't think of a single story that's built on the logical damage Castle leaves in his wake, that doesn't give him an out.
A family member of his victims wants revenge? Well, they were sociopaths to begin with!
Cop wants to bring him in? Well, they're just just losers who can't handle the 'real world'.
And God, every single major villain just kicks puppies to the moon...
Castle may get beaten up, but his idealogical shield is stronger than Captain America's actual shield, and it shouldn't be. It's not for any other character, and they don't need to have him kill innocent people to get through it.
He's not the Hulk, a sympathetic monster. He's a mass murderer, and if there are stories with him that leave you uncomfortable, then I'd call that good writing.
Thing thing with the Punisher is at the heart of the character Frank Castle is just a severely mentally damaged serial killer. You can list of a grocery list of mental problems Frank has. He just focuses all that on criminals. At this point he just can't stop. If it was just about revenge he would have stopped after he killed all those responsible for the death of his wife and kids, but he didn't. He is addicicted to the killing now and without it he would probably kill himself.
There was a nineties comic in which the Punisher took on some shifty Wall Street types and his more recent runs have seen him take down some corrupt politicians.