Yes, but most of those Protestant sects insist on taking the bible literally. ESPECIALLY John, who's their most popular gospel writer. Seems to me like especially the major denominations in the USA are absolutely in love with John, as THE divinely inspired guy who wrote EXACTLY what Jesus said and believed.
Not that it's much easier for the Catholics, although I'll get into their even weirder problems later, since John is in church tradition a major link between early Christianity and late 2nd century guys like Irenaeus and whatnot. In fact, he's pretty much the main link, when those want to claim a chain of information that gives them any claim to know what really happened. If you knock him down to status of just a guy talking BS -- and actually they effectively did -- then you just lost the only documented (ok, "documented" in pious BS fabrications, rather than historically documented) chain of information. Without that, they might as well admit that the sect later known as catholicism was making crap up without any solid foundation for it.
But anyway, if someone takes John seriously and literally, that's exactly what he denies. If you can sin, then you weren't born again in the first place. You may have thought you went through with the rituals, and made up some testimonies about how bad you were before, and spoke in tongues, and all that, and therefore you ARE born again, but John says effectively, "no. If you really were born again, you'd be unable to sin. If you could sin, then you're not really born again, you're one of Satan's guys." Really, you went through the ritual and all, but the criterion for falsifying it says, nah, you weren't born again. I guess it was an abortion again, or something
The ritual obviously fizzled and didn't produce the result you thought it did.
The Catholics, however, took milking the flock to such extremes as to make it basically impossible to not sin, if you have any even remotely normal brain functions. Even going through a day of your life without being in a coma or maybe lobotomized, can get you to break one of the 7 deadly thought-crimes, i.e., deadly sins.
E.g., "pride" is the most grievous of the deadly sins, and STILL defined as basically claiming any merit in any of your accomplishments, instead of crediting God with giving that gift to unworthy little old you. And those last words in that sentence aren't just hyperbole. Even crediting God but claiming or even thinking that you had some personal merit that made God choose you, even praying more or stuff like that, is still landing you in hot water with God. Well, in hot burning brimstone.
And those are deadly sins by virtue of being, you know, impossible for God to forgive unless a priest intervenes on your behalf.
So effectively, the only way to be sure you're saved would be to be killed the exact instant you finished your confession or in the old days bought your indulgence. Because it doesn't take more than a funny random thought to make you unforgivable right back again before you even exit the church.
I think it depends on what gnostic sect you're talking about. The term had been applied to a variety of beliefs ranging from proper mystery cults to just fairly mainstream stuff that the dominant sect didn't agree with.
I don't think any sect will tell its members that some of them just can't be saved, though. It's bad for business, you know?
They can however make other exceptions for the truly gifted. And some did. Those really gifted could figure it out faster, or even theoretically be even able to figure out on their own.
