system
Given the following post, respond as if you're commenting on Reddit:
human
How do you find a singular purpose without turning to religion?

TL;DR: half-educated fool seeks to sacrifice himself for something now that sacrificing yourself for God is no longer an option. Where to go if I also want to avoid humanism?

I've been doing some thinking which, in a nutshell, amounts to the following:

1. The idea of God used to give a singular purpose to life back when it was a dominant force in human consciousness, i. e. all of my instincts, wishes, goals in life, in short - all of my freedom would be subjugated to something external to me. This subjugation is a good thing because it allows me to act with certainty and resolve, since the need for action would not be contingent on my or any other human being's changing desires.

2. Such a faith in God has become impossible for a significant amount of us  and there really is no turning back, i. e. I could decide to perform the role of a person with faith, I may believe that one ought to have faith, but none of that would give me the single-minded release from doubt that actual, living faith would provide. The nonbeliever who has converted to religion has as much self-doubt as the atheist.

3. This leaves two options:

a) Embrace human freedom and live for the sake of myself and other human beings. This is a bad option, because it either:
 - means embracing purposelessness and meaninglessness, since there is no one correct way to go about life and action, including action that we generally tend to value positively, becomes always subject to scrutiny and doubt (it's not enough to do good, you have to know why);
or
 - amounts to little more than an appeal to nature, in other words I do whatever I do because this is who I am as a human being with given desires and needs (caring for myself and the people around me, participating in community, being productive, and so on) - and saying that I am this or that way, doesn't mean I must be this or that way, or that that is the only way to be.

b) Find something else outside myself to subjugate myself (humanity) to.

b) is what I'm interested in here. I'm aware and have read a bit of French existentialists like Camus and Sartre that deal with so-called radical freedom, but they put a positive value on that.

I'm also aware that some sort of totalitarian ideology might be the answer here, but then again those on the right side of the spectrum (fascism, national-socialism) seem to embrace irrationality and nihilism (action for the sake of action, war for the sake of war, the State and the Leader as substitutes for God, because why not) and those on the left (Leninism) seem to still be grounded on the idea of human progress and flourishing (regardless of what happened in practice).

I'm also aware that most of what I said sounds abhorrent, as well as that it might be a problem simply by virtue of the way it is set up and that it may not be necessary to view life this way.

Thanks for reading, would be curious to hear the perspectives of people more versed in philosophy than I am. Been in something of an philosophical / existential slump for a while now.
gpt
I would say that there is a significant underpinning here, which you might do well to abandon. That is: what's so bad about doubt? What's so great about certainty? Embracing doubt is the path to knowledge, confidence, contentment; chasing certainty is the path to disappointment at best, unjustified (and possibly harmful) dogmatism at worst.  

So, again: what has you so worried about doubt? And why do you want certainty so badly?