You must be able to control your horse for your own safety and the safety of others. I get so frustrated when I see people that can not control their horses on the ground or under saddle. If you don't control them it is just a matter of time before you or someone else gets hurt. Controlling your horse doesn't need to be harsh. If you take the time to teach your horse correctly it will make you and your horse much safer.
Somebody told me "A horse needs direction not correction. The handler/rider should know the difference." Take this to heart for your horse's sake and your own. Direction means to teach your horse. If you take the time to teach there will be very little need for correction. When I am "teaching" people about horses I tell them to "1) Ask 2) Encourage 3) Insist". This means that your horse does what you ask every time. Don't let your horse decide if they are going to do what you ask.
A disrespectful horse can be a dangerous horse. Teach your horse to respect your space. Your horse should not enter your personal space unless they are invited. If they are not invited they should be about an arm's length away. You should be able to easily back them away from you if they get too close. If they don't back away when asked, teach them to back away when asked. You should not have to move away from your horse, they should move away from you. When a horse gets in your space and you move away from them you have allowed them to be dominant (to be the herd leader). You need to be the dominant one. You have to be in charge.
Take time to teach your horse good ground manners. Every horse should be able to stand quietly when they are tied or in hand. Your horse should not be walking over the top of you. Give your horse a little nudge with your elbow if they are walking too close to you. If necessary carry a riding crop or a lunge whip with you when you walk your horse. If they are getting ahead of you or crowding you, a little tap on their shoulder will get them to move away. A horse stepping on you will hurt (speaking from experience) so make sure the horse is behaving and respecting your space.
When you ask your horse to do something make sure they do it. When you ask and don't follow through with the request you are allowing your horse to be disrespectful. If you allow your horse to say "no" or "I don't want to" this response will follow you into a dangerous situation. When you ask your horse to stop, teach them to do it immediately not 10 steps later, not even 2 steps later. If you are lunging your horse and you ask for a speed increase or decrease make sure you get it, teach them to do it. If you can't control your horse on the ground you won't be able to control them under saddle.
Horses should also be under your control when you are in the saddle. You have to be able to stop your horse and you have to be able to turn them. If you get into trouble and you can't control your horse you are in danger and so is everyone around you. Again, take time to teach your horse to respect you in the saddle just the way you did on the ground. There is nothing worse than being on a trail and coming up on other riders that can not control their horses. I have seen an out of control horse run over people on the ground; I blame the rider not the horse. It is the rider's responsibility to teach and control their horse.
Don't let your horse control you or the situation, a horse in control is going to make bad decisions.