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(Some of) my players are trying to role play in a meta-gaming sort of way.

For instance, I had an array of weapons in a dungeon, and when they took them, they had to make a Wisdom saving throw, else they feel ridiculously guilty and take 1d4 psychic damage. A few of the players tried continuously take stuff down, even though they had failed the Wis save. I tried to discourage them from this a few times, but they seemed to meta-game in the sense that: "Oh boy, my level 3 character has 21 hit points left. I'll take another one." Pretty much, they were willingly hurting themselves for a little more loot. I was trying to give them the cues that they should feel guilty, drop the longsword and walk away, but they seem to think about it in a different way.

How am I, as the DM, supposed to approach this issue?

When you dictate emotions to a player, dictate mechanical effects of those emotions.

Assuming good faith here - your players are not deliberately metagaming or ignoring your narration. They may have just come away with the impression that 1d4 psychic damage is the full and complete effect of the guilt their characters felt.

If you want to compel an action from them, take control away from them. Make it clear where the effects of the spell end and their agency begins. D&D has a lot of mechanics which punish players with heavy things (like dead characters) if they fail an encounter. This creates an expectation that player characters will, most of the time, cooperate and do what is best for the team.

In that situation, instead of giving players vague directions and expecting them to then choose to act in a way that is against what they perceive to be the party's best interest, you should make it clear what actions they are allowed to take or not take, and then leave them free to roleplay their character as they like in the space that remains.

When they fail the wisdom save, you say:

You are overwhelmed by inexplicable guilt. You put the weapon back on the rack, and back out of the room, and resolve not to touch the weapons again. You take 1d4 psychic damage from the lingering guilt even afterward.

Then, if they try to take the weapons again, do not let them repeat their save, instead, re-iterate the effect of the previous failed save, and make it clear that you won't budge.

You reach out to take the weapon, but the inexplicable feeling of guilt returns. No matter what you do, you cannot bring yourself to do it.

That said, you should only dictate emotions if they come from a magical source

In most circumstances, players are the final authority of their character's inner life. Dictating emotions or actions from a character without a clear external force acting on them is robbing them of their one and only source of narrative control within the game. Don't do it.

If you want them to feel guilty for a reason besides magical mind control, give them a reason to feel guilty, then accept however they choose to roleplay in the face of that reason.

Making decisions on the basis of hit points is not a concerning exercise of metagaming.

Think of it like this. If you'd said:

As you grasp the weapon, arcs of electricity pulse through your body! Your limbs convulse hideously, out of your control, and you think you feel your arm break! Take 1d4 lightning damage!

or:

As you lift the weapon from its rack, a series of clicks echoes through the wall behind it, rapid-fire, snap-snap-snap-snap-snap! One of the ceiling tiles pivots all the way around and in that brief second it's exposed a launcher fires a wickedly barbed dart at your unsuspecting neck with terrifying accuracy! Take 1d4 piercing damage!

they'd probably still keep grabbing weapons despite your concerning descriptions, wouldn't they? The same as they'd stand and fight rather than run away after the first hit from a goblin's 1d4 dagger, no matter how it was described. The damage is the only thing they think is a game object, therefore it's the only price for getting what they want and they're willing to pay it.

If this isn't a good idea For Secret GM Reasons, you need to show it with something more than just the numbers, either foreshadowing consequences down the line:

There's an inscription running all around the ceiling of this whole complex, a mantra describing the virtues and acts of Tan'O'Zul. "Tan'O'Zul shines in the heavens." "Tan'O'Zul lays waste to our enemies." "Tan'O'Zul judges the guilty." By what must be sheer coincidence that last one has lined up exactly over the weapon racks.

You're already feeling guilty. You want to keep going?

Hinting that things will escalate mechanically with a "safe" first step:

Well, you're already feeling guilty, and this only makes it worse. Take [2d4 psychic damage/1d4 psychic damage and a level of exhaustion/1d4 psychic damage and a mild curse that imposes a -1 penalty on mental (int/wis/charisma) rolls].

Or hinting that things will escalate mechanically with an in-game warning. This was a trap deliberately prepared, right?

You reach out again and purple runes burn themselves onto the wall. IF GUILT WILL NOT STAY YOUR HAND, DESPOILER, THERE ARE HARSHER THINGS. RETURN WHAT YOU STOLE AND THERE MAY YET BE MERCY.

(For added effect, only the people who have "felt guilty" can see the writing.)

If this isn't a good idea for Less Than Secret GM Reasons, such as that the party talked their way past some orcs to get deeper into the dungeon and these are their weapons, or the dungeon is a desecrated tomb of the Order of the Emerald Heart which the party was hired to clear out and these are their weapons, you might just want to mention that.

Guys, these are [the orcs' weapons/the burial weapons of noted Knights of the Emerald Heart]. Do you think [Warchief/Knight-Captain] Relegar isn't going to notice?