Is there anything that cannot be criticized, or cannot be treated with scepticism ...

Is there anything that cannot be criticized, cannot be treated with scepticism, or/and cannot be doubted by?

No

What do you mean by “cannot”? It is clearly physically possible to doubt anything, I would say it is ethically and logically okay so long as it is done with intellectual honesty, but in many cultures some items are off limits if you don’t want to get whupped.

Maybe mathematics?

I can doubt mathematics. Watch me: “I hereby doubt mathematics!”

That wasn’t hard.

One thing that definitely can be criticized: One liner OPs in GD.

We don’t even have the possibility or knowledge to criticize. Or we are sure that it is true.

Look at the threads through a screen with 100x100 display resolution rate. So you don’t see any one line thread at all.
or copy what’s written in thread to a notepad file and get the windows smaller. So you don’t see any one line thread at all either.

Your response just doesn’t seem to add up.

I’d draw the line at solipsism. There’s a point at which you leave scepticism and move into mental masturbation.

Gravity comes to mind.

I don’t know. I’ve seen some things that make me question (albeit momentarily) even things as obvious as Descartes “I think therefore I am”, which should be an otherwise indisputable truth, right?

I think that it’s okay to be skeptical to a certain degree. We don’t have to pretend that we have some sort of omniscient ability. I will try the best that I can to hold the most rational position given the available evidence. If you come to a different conclusion that is fine.

At certain points in my life I’ve felt that doubt was not okay - when I did eventually doubt, the damage and the shake up was fairly life-altering (at least IMO). So now I try to be more open with my beliefs.

Au contraire, it’s integral to the discussion.

These one liners are getting exponentially worse.

We need to act radically - root them out wherever they’re found!

I think you are taking something real and adding imaginary issues to make the whole thing unnecessarily complex.

Pretty derivative, too.

But when taken together they are surely greater than the sum of their parts.

Cosign.

Cogito ergo sum. (People have given quite serious consideration to this question before, you know.)

Do you mean the tendency of earthy material to seek its natural resting place at the center of the universe (Aristotle), or the centripetal push produced by an aetheric vortex (Descartes), or the inexplicable attractive force operating at a distance between masses (Newton), or the distortion of the geometry of space caused by mass (Einstein), or, well what? Maybe something no-one has though of yet. Before Newton nobody believed in some force called gravity, and we don’t believe in the force he was talking about now. Most certainly it is possible to have doubts about it, Whatever you think* it* may be…