Because the rate of new users getting scammed would be ridiculous otherwise.
Why? Explain please. I think that this is a baseless statement.
Use your head. Some people get scammed even by user accounts that already have red trust; do you really think it would be better if there was no red trust?

If I were fooled by a scammer, only I would be responsible and I think it's right.
Let's toss everyone into chaos. After all if we can protect some users, why should we? It's their responsibility to protect themselves.
That is nonsense that can't be applied to this.
Sorry, I will repeat myself, why? Could you explain how you see this? I can. I never trust someone by default. I know that there are many good people on this forum, but still, by default I don't trust anyone. I will check everything by myself. At least, I need to do my own research. But, by default -- never.
You're using quotes that you think you understand, but you really don't. What exactly would you verify instead of trusting?

Enough with this fallacious nonsense.
Who are you going to trade with, some random that never did paypal-to-btc or someone who has 100+ such succesful changes? Oh right, don't trust verify the 0-trade-newbie offering reversible methods of payment.

<- shows how absurd your attempt is.
I see your point, and the answer is -- the escrow.
Yeah, "Who you can to trust if you do not trust anyone?", but still, if an escrow have a thread (not self-moderated) and there is a lot of feedbacks, so after checking these feedback and the account owners I will make my decision to work with that person or not.
The difference between a seller with 100 trusted feedback, and an escrow with 100 trusted feedback is what exactly? You'd choose the escrow because he/she is an escrow?
* Lauda facepalms
So, why so many years I "trusted" you by default? ("You", in the context of DT1)
Here's a simple solution: Remove Defaulttrust from your trust settings and lock this thread. I'm not sure whether this is utopian-styled "we can educate everyone on the planet not to be naive", or dystopian-styled "throw everyone infront the bus, it's their responsibility" thinking. Whichever it is, it is wrong.
Edit: Many typos.