The bolded part is the preachy part. I know it seems to escape you because you're not religious yourself, but I suppose most evengelists don't consider themselves to be preachy for sharing "the truth".
Like I said, I was religious when I first saw this, and was not offended at all. Nor did I feel like anyone's beliefs were being pushed on me.
I hate to break it to you, but it's preachy to force your beliefs on others. It's true that the episode tries to hide what it's doing by having these aliens mistake Picard for a god, but it does a pretty bad job of it, as Star Trek tends to do.
True that it does, but I never felt a belief was being forced on anyone. I didn't even really see any beliefs expressed except that superstition and fear are bad things, which I'd have to agree with. Barron speaks of all the reasons why Picard should act as their God, so as to prevent things like holy wars and religious squabbling, which was almost guaranteed to happen with any religion.
Religion is such an iffy topic for Star Trek. Especially so when you consider the question of aliens affecting primitive cultures naturally arises. Some people think that our cultures were affected by aliens! I think it was a decent story showing some interesting possibilities for a civilization.
The implication here is that it was a great achievement for these people to give up all religious belief, which Picard refers to as "supernatural". There's also nothing in his dialog that suggests it's just about the aliens worshiping him.
That's only because you're reading just a snippet that I picked (because it seemed like the one people thought was preachy). Here's a larger excerpt:
BARRON
(nods)
They are not normally a violent
people... but these are
extraordinary circumstances.
They're trying to comprehend what
they believe to be a god.
STAR TREK: "Who Watches... " REV. 8/14/89 - ACT THREE 35.
69 CONTINUED: (2)
PICARD
Recommendations?
BARRON
The Mintakans wish to please the
Overseer, but they can only guess
what he wants. They need a sign.
PICARD
Are you suggesting...
BARRON
(nods)
You must go down to Mintaka Three.
RIKER
Masquerading as a god?
PICARD
Out of the question. The Prime
Directive --
BARRON
Has already been violated. The
damage is done; all we can do now
is minimize it.
PICARD
By sanctioning their false
beliefs?
BARRON
By giving them guidelines...
letting them know what the
Overseer expects of them.
PICARD
I cannot -- I will not impose a
set of commandments on these
people. To do so violates the
essence of the Prime Directive.
BARRON
Like it or not, we've rekindled
the Mintakans' belief in the
Overseer.
RIKER
(to Barron)
And you're saying that belief will
eventually develop into a
religion.
STAR TREK: "Who Watches... " REV. 8/14/89 - ACT THREE 35A.
69 CONTINUED: (3)
BARRON
It's inevitable. And without
guidance, that religion could
degenerate into inquisitions...
holy wars... chaos.
STAR TREK: "Who Watches... " REV. 8/14/89 - ACT THREE 36.
69 CONTINUED: (4)
PICARD
Your own reports describe how
rational these people are.
Millennia ago, they abandoned all
belief in the supernatural. And
now you're asking me to sabotage
that achievement... send them
back into the Dark Ages of fear
and superstition.
(adamant)
No. We must undo the damage we've
caused.
Superstition definitely applies here because they're talking about Picard as a god figure. It doesn't get any more irrational than that. He wouldn't have been sending them into a more enlightened age by any means, so he was totally right. It wasn't a belief at that point, it was fact.
How anyone cannot see the anti-religious bent in this episode is beyond me. They even portray the crazy murderer fundamentalist stereotype at the end when that dude wants to kill picard to prove his belief.
Perhaps it's anti-false-god-figure, but that's not really the same thing. Also, not everyone was like Liko. But he was the proof that the idea of a false god would have dire consequences on their society.