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Reproducible Example

In [1]: DatetimeIndex(date_range('2000', periods=2).as_unit('s').normalize(), freq='D')
---------------------------------------------------------------------------
ValueError                                Traceback (most recent call last)
File ~/pandas-dev/pandas/core/arrays/datetimelike.py:1912, in TimelikeOps._validate_frequency(cls, index, freq, **kwargs)
   1911     if not np.array_equal(index.asi8, on_freq.asi8):
-> 1912         raise ValueError
   1913 except ValueError as err:

ValueError: 

The above exception was the direct cause of the following exception:

ValueError                                Traceback (most recent call last)
Cell In[1], line 1
----> 1 DatetimeIndex(date_range('2000', periods=2).as_unit('s').normalize(), freq='D')

File ~/pandas-dev/pandas/core/indexes/datetimes.py:335, in DatetimeIndex.__new__(cls, data, freq, tz, normalize, closed, ambiguous, dayfirst, yearfirst, dtype, copy, name)
    332         data = data.copy()
    333     return cls._simple_new(data, name=name)
--> 335 dtarr = DatetimeArray._from_sequence_not_strict(
    336     data,
    337     dtype=dtype,
    338     copy=copy,
    339     tz=tz,
    340     freq=freq,
    341     dayfirst=dayfirst,
    342     yearfirst=yearfirst,
    343     ambiguous=ambiguous,
    344 )
    346 subarr = cls._simple_new(dtarr, name=name)
    347 return subarr

File ~/pandas-dev/pandas/core/arrays/datetimes.py:360, in DatetimeArray._from_sequence_not_strict(cls, data, dtype, copy, tz, freq, dayfirst, yearfirst, ambiguous)
    356     result = result.as_unit(unit)
    358 if inferred_freq is None and freq is not None:
    359     # this condition precludes `freq_infer`
--> 360     cls._validate_frequency(result, freq, ambiguous=ambiguous)
    362 elif freq_infer:
    363     # Set _freq directly to bypass duplicative _validate_frequency
    364     # check.
    365     result._freq = to_offset(result.inferred_freq)

File ~/pandas-dev/pandas/core/arrays/datetimelike.py:1923, in TimelikeOps._validate_frequency(cls, index, freq, **kwargs)
   1917     raise err
   1918 # GH#11587 the main way this is reached is if the `np.array_equal`
   1919 #  check above is False.  This can also be reached if index[0]
   1920 #  is `NaT`, in which case the call to `cls._generate_range` will
   1921 #  raise a ValueError, which we re-raise with a more targeted
   1922 #  message.
-> 1923 raise ValueError(
   1924     f"Inferred frequency {inferred} from passed values "
   1925     f"does not conform to passed frequency {freq.freqstr}"
   1926 ) from err

ValueError: Inferred frequency None from passed values does not conform to passed frequency D

In [2]: DatetimeIndex(date_range('2000', periods=2).as_unit('ns').normalize(), freq='D')
Out[2]: DatetimeIndex(['2000-01-01', '2000-01-02'], dtype='datetime64[ns]', freq='D')

Issue Description

I don't think the first case should raise?

Expected Behavior

DatetimeIndex(['2000-01-01', '2000-01-02'], dtype='datetime64[s]', freq='D')

Installed Versions

INSTALLED VERSIONS ------------------ commit : 954cf55938c50e34ddeced408d04bd04651eb96a python : 3.11.1.final.0 python-bits : 64 OS : Linux OS-release : 5.10.102.1-microsoft-standard-WSL2 Version : #1 SMP Wed Mar 2 00:30:59 UTC 2022 machine : x86_64 processor : x86_64 byteorder : little LC_ALL : None LANG : en_GB.UTF-8 LOCALE : en_GB.UTF-8 pandas : 2.0.0.dev0+1168.g954cf55938 numpy : 1.24.1 pytz : 2022.7 dateutil : 2.8.2 setuptools : 65.7.0 pip : 22.3.1 Cython : 0.29.33 pytest : 7.2.0 hypothesis : 6.52.1 sphinx : None blosc : None feather : None xlsxwriter : None lxml.etree : None html5lib : None pymysql : None psycopg2 : None jinja2 : None IPython : 8.8.0 pandas_datareader: None bs4 : None bottleneck : None brotli : None fastparquet : None fsspec : None gcsfs : None matplotlib : None numba : None numexpr : None odfpy : None openpyxl : None pandas_gbq : None pyarrow : None pyreadstat : None pyxlsb : None s3fs : None scipy : None snappy : None sqlalchemy : None tables : None tabulate : None xarray : None xlrd : None zstandard : None tzdata : None qtpy : None pyqt5 : None None