Is this safe?

Agreed...

But it doesn't make sense to me to purposely buy a weak halter... waste of money.

Horses prefer being naked and streaking across the grass anyway, right?

My horses aren't hard to catch in the pasture. They come right up to you. It's when they get out and are heading to the highway that I have a problem with.

They are watched, they are not allowed to be outside unless someone (me or my dad) is home to put them out and watch them.

They also don't wear their halters in their stalls.

Mine are snug enough that their hooves can't get hooked. And there is nothing in their pasture, no trees or bushes. We have smooth wired fencing or electric fence.

I had a gelding come in with a hole in his face that needed stitches. No halter, just playing.
I will sometimes leave halters on when inroducing new horses, even though they spend at least a month separated by a fence before the introductions. I have intervened in horse fights.
I only use well fitted leather halters.

No I didn't forget that there's an alpha mare, but mares usually don't play. If it's establishing a hierarchy, they wouldn't be nipping at the halters. They would be biting at the neck, legs or sides but more likely kicking. They would likely leave serious marks. When playing, they may make contact but not really bad marks.
As for the stepping in, maybe I misunderstood what she meant. When we feed ours they are next to each other but in seperate stalls but close enough to make contact, such as biting. If she is feeding them in the pasture then I wouldn't step in. I would let them settle it on their own or seperate them at feeding time. I have fed our in the pasture by spreading out their bowls but I would have to 'protect' our youngest mare. The others would make her move away from her bowl and take her food. They learned that it's best not to challenge me though.

That's not necessarily true though. My lead mare reminds my filly of her place with a look, pawing, and will sometimes lash out at her. Horses will aim for the face on occasion. It is also likely that that they aren't nipping the halters, it's just that the halter gets in the way. It is absurd to say that horses establishing the pecking order will only do XYZ, and horses playing will only do ABC. O_o

I have not ever left a halter on a horse in the pasture. If anyone ever witnessed the aftermath of a horse hung up by a halter you'd never leave one on a horse either. I don't know who the horse's owner was, but the horse was dead and there was a full circle of blood about 20 foot in diameter all around the horse. This may be a shock to read, but it may save another horse from the same end of life experience.

We don't leave halters on our horses, but we will keep the fly masks on them in the summer time. As long as your horses have plenty of room to get away from each other if they want, and the food is spread out when you feed then they will probably be ok. They are going to play, fight, & get scratched up that is just what horses do.

What's not true? Mares don't play? They wouldn't be nipping at each others halters? They might go for the face and the halter gets in the way? If it's hierarchy like you say, there are the warning signs: ear pinning, the "look", and tail swishing. Also there's a difference between nipping and a decisive bite attack.

No it's not really that absurd. It's not that hard to tell if they are playing or if they are really fighting. The problem is that we can't actually see it and we are speculating with what was said. You have your opinion and i'll keep mine that they are probably playing.

I will agree with the majority of people who posted, the horses are either playing or establishing dominance.

Are these horses making contact when they kick?
If one horse is particularly agressive to the other, I would separate them. My instructors yearling Hawkeye is a very submissive horse, and his herd-mates took advantage of that. Annie and Joey would bite him and made contact on several occasions. I was cleaning out the run in shed one day and Annie wanted a drink. Hawkeye was "in her way", so she kicked and nailed him right on his left hock. My instructor decided to move Hawkeye to the other pasture that day, and has much less trouble with new herd mate, Monty.

If they aren't making contact, and they don't seem to be agressive (ear pinning, pawing, "intent to hurt" biting, tail swishing, etc.) I would leave them be. Horse play looks similar to fighting, but in reality, playing doesn't hurt either horse. Fighting is intended to hurt (usually just enough to say, "hey, I'm in charge, so do what I tell you".

And I'll be another advocate to take the halters off. Unless your horses are so difficult to catch it takes you two hours to actually get the halter on the horse, don't leave it on. (If this is the case, there are major training issues that need to be adressed.)

The only time I've ever seen somebody leave halters on horses was when a new horse was being introduced to a herd. All of the horses had halters left on in case the newbie needed to be removed from the pasture. All the horses were supervised by myself and my instructor. The halters were removed before we left.

What do you do when a horse has escaped their pasture? And are prancing around your lawn?