Suffering is generally regarded as something bad because the very short term future looks hopeless and bleak. When we are in pain, we are quite incapable of looking away from our suffering or even understading why are we suffering in the first place. Just think about any physical pain that you have experienced and you will remember how overwhelming it felt.
However, as many great thinkers have realized, suffering is not only natural, but necessary, and one can obtain so much from it. Viktor Frankl, in his book Man´s search for meaning, presents a theory that the inmates in the concentration camps that gave meaning to their suffering were more likely to survive that those who only saw pain and destruction on their suffering.
I am a firm believer that suffering is the best (and even only) tool that allows us to really make our lives meaningful. I will never run from it, instead, I shall embrace it and welcome it.

Depends on what you mean by suffering. Do you mean being in a state of uncomfortableness or displeasure that will eventually dissapate? I consider some of the tests I had to take back in the day suffering under that definition. =)

I would say that type of suffering is not objectively bad. Having emotional states that we do not like can motivate us to actions that could be called, "good".

But what about suffering that is permanent? Like losing a leg? Having irrecoverable brain damage? Having a child die on you? At a first glance, I lean towards those things as being objectively bad. If I could save someone from such a fate, I would do so in a heartbeat without any reservation or regret. Such suffering is not I think the emotional state, but the diminishing of one's capabilities and person.

I lean towards those things as being objectively bad. — Philosophim

why is it objectively bad in this instance?

I would disagree somewhat I think not only the close future but the long term one are all full of suffering, I'd say it is not something to embrace, it is something already in the living condition and always will be, it can only be masked never truly removed, hence it is not a tool, it is us.
meaning, it is not something good to embrace for me at least, because it is not something embraceable

Pain is obligatory, suffering is optional.

pain is a part of suffering

There are quite a few ways to define the word "bad". If by "bad" you mean improper or abnormal, then I would agree that suffering is a normal part of life that one should expect to encounter.

You could also say that a "bad" thing is intolerable, or incapacitating. I think suffering has to meet this definition in order to serve it's purpose as a deterrent. Nature has given the mind both positive incentives and negative incentives. Positive incentives are pleasurable feelings that we want to pursue. Negative incentives are unpleasant feelings that we want to get rid of.

Physical pain is obviously a negative incentive. The purpose of physical pain is also obvious; it helps us avoid damaging our bodies. Physical pain would no longer serve its purpose if we somehow made peace with it; if we no longer considered it to be bad. So in that sense, suffering has to be bad by definition.

If suffering is objectively bad and someone disagrees then you are saying that they are factually incorrect. If the person who disagrees approaches suffering in a way that enables them to cope with it in a better way to you, they're still factually wrong. So they have a better approach to suffering than you but you're correct and they're wrong. Do you agree this could happen and if you do agree, doesn't this framing make the initial question of whether suffering is objectively bad rather pointless?

why is suffering regarded as bad? — Augustusea

Because, essentially, there's the issue of how much. Can suffering be quantified?

The term 'tragic' would perhaps better describe that type of suffering from which no personal growth is possible.

Suffering: the awareness that a system is insufficiently resourced to fulfill its predicted/expected energy (effort and attention) requirements.

Augustine and that tradition say suffering is a privation of reality. Von Balthazar was a traditionalist who thought that all evil was substantial, but it's usually the Gnostics who say such. If we avoid that terrain, the topic of this OP is sticky, as I think Judaka pointed out best above

Suffering an inevitable part of life and existence itself, is mainly subjective, yet everyone who exists has it happen to them — Augustusea

There is no permanent solution to physical hunger. Every one ever born has to eat regularly. This need is inevitable, non-negotiable.

We also have to breath, even more regularly.

We also have to sleep, a third of our life.

We also have to use the bathroom.

We also have sexual needs.

We don't fall in to despair over these needs. We don't waste time on Schopenhauer books. We don't declare life hopeless because of such needs.

Instead, we are sensible. We manage these needs.

Suffering is no different. It's just another mechanical function of the body which requires ongoing management.

Observe if you will how fancy philosophers try to turn this common sense situation in to some kind of complex issue requiring their services. Just another pile of nonsense.

Such suffering is not I think the emotional state, but the diminishing of one's capabilities and person. — Philosophim

Suffering is not the diminishment you refer to, but one's relationship with that diminishment.

Suffering is not losing the leg. Suffering is the state of mind which rejects the loss.

This is good news! Nothing can be done about the lost leg, but something can be done about the state of mind which rejects the loss.

Suffering is indeed objectively bad, since nothing else can possibly be bad and the very meaning of bad is in suffering. Whenever you deem something to be bad, you mean you dislike it either because it produces an uncomfortable feeling, that is suffering, in yourself or in others, or you think it might lead to something bad, that is, ultimately cause discomfort or suffering. (Discomfort is just a mild form of suffering.)

Of course we shouldn’t try to avoid all immediate suffering, since it is often necessary to suffer a little in order to avoid a greater suffering later. You suffer through work so you can make money and avoid starving. But in itself, when disregarding the outcome, suffering is bad and only bad. Why would anyone want to suffer if it had no positive results whatsoever, if it led to nothing? (The objection of sadomasochism is not relevant since the sadomasochist derives pleasure from suffering, so it is not really suffering at all.)

why is suffering regarded as bad? is it only because we have not a good feeling when it happens to us? are feelings even rational to consider in this situation — Augustusea

Feelings are certainly relevant since the goal of everyone’s life is to obtain good feelings which is the same as what is usually called happiness. Happiness is the ultimate goal for everything we do. We want to achieve it for ourselves or for others.