That is incorrect. Science could easily find evidence that at least some spiritual entities exist, if the spiritual entities are willing to cooperate to achieve the goal of acquiring empirical evidence of their existence.
Think of it this way, assume that a scientist had the hypotheses:
- God does not exist.
- No supernatural power or entities exist in any way.
Now further assume that 1. is untrue and God exists. If God wanted he could help the scientist at once to find empirical evidence that 2. is untrue. He would just have to tell him “Whenever you touch a human no longer dead than 7 days and with all major body parts present and ask me loud to bring him bakc to life, it will be done. Use this to demonstrate all your fellow scientist, that something supernatural must exist.” Scientist grabs his colleagues, they are off to the next morgue and he repeats it as often as necessary that all natural explanations can be excluded (which would not be very often, actually once bringing a human dead since 7 days beck to life under close observation would be enough), empirical evidence exists that 2. must be untrue.
The only possible reasons, why science has not found empirical evidence of supernatural entities or God?
a. they do not exist
OR
b. they do not want or are for unknown reasons unable to provide the empirical evidence
(BTW, thats my own experience with people claiming to be in contact with supernatural entities - whenever i suggested a simple test to prove their existence, people claimed that the supernatural entities see no reason why they should cooperate.)
Assuming catholicism is right about the existence of God, angels, demons and the devil, then at least God is unwilling to provide empirical evidence (being unable not being an option for Him) and angels, demons and the devil either unwilling or unable. The further conclusion would be, that since God is supposed to do everything in favor of our salvation, that He is of the opinion that lacking empirical evidence of His existence is better for our salvation than having empirical evidence. Reminds me of “Blessed are they that have not seen and yet have believed.” (assuming seen = empirical evidence is valid interpretation)
As having evidence of angels, demons or the devil would also constitute something close to existence of God (if those catholics got the angel, demon and devil thing right, their God hypotheses is suddenly rather plausible), it would be no surprise if God would order/force angels, demons and devil to also avoid providing empirical evidence.