A miracle is what is not naturally possible. It is a supernatural occurrence. It is paranormal. It's an act of God.
Religion uses alleged public miracles as evidence for the truth of its claims.
Belief in secret miracles is dangerous for it says we should neither trust or mistrust anything for we don’t know when they happen or how much they happen.
If clear miracles happen, it is supposed that secret ones happen too. Indeed one would assume that they happen far more often.
According to some objectors, “Clear miracles happen and are supported by evidence. God sends them and is well-organised. We know nothing about the unknown ones, and it seems we should not believe they happen, for there is no evidence that they do.”
That is only an assumption. Also, many miracle reports are not heard of outside a tiny circle of people. They are secret. To make belief in miracles safer, you need to refute alleged hidden miracles beyond all doubt.
What of secret miracles that nobody at all has experienced? If you say they are possible then you cast doubt on all you take for granted. And to say they are likely is to deny the validity of any evidence you give for anything. Eg, maybe the Devil put Johnny's fingerprints over the stolen vase.
You could have a known miracle that you won’t see as such until later. Most known miracles only become recognised in time. It sounds desperate to say that a miracle only happens when it will be found to be such. When? Ten years? A hundred?
You should know if the miracle was real the minute it happens without testing and investigating.
Another problem is that all miracles look silly at least to some people.
If God can do things such as make the sun spin at Fatima instead of feeding starving children or if he gets Jesus to walk through a wall instead of using the door then why can't he do secret miracles?
A miracle that you don't know of that stops you running over little Charlie is more important than one like that.
To admit public silly miracles may happen, is to say that it is possible that the sun has died and the sun we have now is a replica. To say that strange and silly secret ones happen is to make this far more probable than ever!
Assume we should believe in miracles. Nobody who believes in miracles, who is sincere and who has a little logic, ever says a miracle HAS happened. It would be better to say is that a miracle HAS PROBABLY happened. The reason is that there could be natural laws that do the miracles and these laws have not been found yet. And there are explanations for alleged miracles, perhaps alien super-science or something, that don’t need the supernatural. You cannot ever show a miracle report was correct beyond all reasonable doubt. So every miracle is a secret silly miracle in the sense that you are not definite that it is a miracle. You don’t even know if it is probably a miracle. Again, miracles undermine all evidence.
Science shows that antibiotics work. Or does it? What if they are useless and it is a perpetual miracle at work? That would explain why people get better. Researchers all agree that to view God as constantly or perpetually suspending natural law makes science useless and futile. Religionists would add blasphemous. Even the suggestion that God could be perpetually suspending natural law or alternatively that what looks like a natural cause in fact is not (eg - if antibiotics do not affect the immune system - and the response of the immune system is not down to them but a miracle) ruins science. Science works hard to verify. It keeps checking. It has too much work to do as it is. So do not add to it with miracles and supernatural allegations.
You could say that even though x was exposed to y coughing over her, the flu virus she got was not from y but was a miracle one. If you claim it's a right to believe in non-secret miracles then it's a bigger right to believe in secret ones like that. Why? From the human point of view, there will be less controversy and bother for people. Secret miracles do not attract fanatics. They do not give false hope to the desperate - or become an excuse for them to give it to themselves. Charlatans will not be able to prey on people who believe only in secret miracles. There will be no time wasted on them for they cannot be investigated.
If a miracle is reported, you never know what the miracle really is. For example, a secret miracle altering people's memories could be behind the risen Jesus visions. Assuming Jesus rose is too much. You don't need to.
From the intellectual point of view, there is no reason to believe in secret miracles. As there is no evidence for them, we simply assume they don't happen. Miracle claims of every sort undermine the very evidence and support they depend on! They advance the superstitious mentality.