For arguments sake imagine that your consciousness is transferred into a simulation that runs at a highly accelerated rate so you can experience a very long existence. The custodian of the simulation is benevolent, it tries to keep you happy, lets you shape the world in whatever way you want but the one hard rule is that you are not allowed to end.
You will probably have an awesome time for the first few hundred years. So many fun experiences you could only dream of before. You can explore the stars, turn the world into paradise, come up with new forms of art that no one has imagined.
After a few thousand years things might start getting a bit samey but you will still find new things to do. But how about after a few million years? Or billion? It might start getting pretty boring. You have done all the fun things countless times and all the terrible things too just to do something different. But your looooong adventure is only beginning! There is no exit button. Welcome to hell.
The scenario is not completely implausible, agreed? I think one of the Iain M Banks novels had something similar going on. I think the custodian there was evil but I am arguing that on the looong run that makes little difference.
One might argue that they would transform themselves into something that can tolerate the infinite existence but I call that cheating, such a thing wouldn't really be you anymore. And the custodian might see it that way too.
So if we're speculating here your argument is that boredom is a curse. At my age I'm already bored every single day of my life.
I'd rather be bored than be dead. But again this is speculation. I'd rather be bored for 50 years than die at 50 but would I be the same at 5 billion? Truthfully nobody knows. Even 50 Years is a long time to be bored but if you're not bored at 50 what makes you suddenly conclude that 5 billion is too much?
There's no evidence or weight behind this philosophy. Boredom does not equate to being cursed.
The ridicule the comment made is for a mindset that actually happens right now, talk to some retired boomer relatives. A lot of them have had actuarial consultations and some of those are treating it almost like gospel, like the other comment wishing he could do the same given 23andMe reporting. This leads to them depleting their savings (mostly held up in "safe" investments that aren't expected to grow or shrink much over the relevant timespan) at some rate so that it gets close to $0 by the time they can expect to die. Some older people have already made it long enough to go past that point, and they get into the same situations that retirees without any savings get into. i.e. you hear about old ladies subsisting on dog food because their only source of income is a small social security check.
A better mindset is the one used by the FIRE crowd, which applies just as well if you're "retired" at 30 or 60: recognize index funds are not just pretty safe but also give a pretty high confidence minimal rate of return, plan for average x% returns per year, and don't withdraw more than x% for income, so that your savings never decreases but in fact increases. This way you can retire whenever your savings hits the right number to support your required income indefinitely, rather than retiring when your savings hits the right number to provide income only for the next X years until you die.
(I shouldn't have to say it but will: this is a theoretical optimal modeling strategy, reality will be messier, any real plan should analyze possible setbacks and ways to deal with them -- the easiest way typically being to seek work again for some period of time, which tends to be easier the more biologically young you are. And of course, regardless of biological immortality or whatever, you could be an unlucky passenger in a car driving down the freeway when a random brick from a truck in the oncoming lane comes loose and collides with your head.)
But whether it's good or bad is something that only an individual can determine. It's more/less along the same lines as the question "is life worth living?"
Additionally "living forever" isn't invulnerable immortality where you are doomed to float around alive in the solar system long after the sun has inflated and pulverized the earth as a red giant... You'll still die well before that.
You can also always choose when to kill yourself, whenever. Logically any form of "living forever" described as a scientific possibility is actually more of a "you can choose when you die" or a "you can live much longer than normal"