I don't think anyone is saying to attack someone. I think we can all agree that telling someone that they are abhorrent at the game and to avoid any content that involves other people is not an acceptable way to behave. From what I have seen, no one here is advocating for attacking and demeaning a player for not being perfect. Being hostile will get no one anywhere.
And there's also a difference between lack of skill and comfort, as Kolaina has mentioned, and going out of your way to be intentionally bad. If someone isn't doing optimally, whatever, it's not a big deal. No one who does pug content expects everyone to be at the top of the game. Skill varies and that's okay. It's the effort, or lack thereof. The refusal to learn, grow, and apply yourself.
But to be accepting, encouraging, and even defending people who simply do not want to try and are willfully being carried? That's not okay, either. It may not phase you. That's fine, it doesn't necessarily have to if it's just you they are playing with. But that shouldn't discredit the people who it does bother. And it shouldn't be defended. If it doesn't phase you, then don't stand up for the person when someone else speaks up. If they're getting nasty, sure, keep them in line, but advice is not inherently rude. Enablers don't help any situation. And if someone is trying to learn and grow, telling them that they're "doing fine" when they're struggling, instead of offering honest advice to help, stunts growth and is more harmful than anything else.
And that, I find, an issue. I understand I can't choose how someone takes advice. But if they are willfully ignoring advice given, that's a refusal to grow and learn. Solicited or not, a lot of time, the advice players give is out of the goodness of their heart. They want to help, not attack. So I think players who get angry at advice are honestly just as bad as players who don't put in effort.