Whether or not celebrating Hallowe'en is bad depends on what you think you are celebrating.
If you really do think you are celebrating Satan and evil, then that would be bad although probably based on a lie about the festival.
If you think you are celebrating some ancient celtic festival of the dead, that is also probably based on a lie but all the same is not inherently evil.
If you think you are celebrating a purely secular festival just for a bit of fun, that isn't evil either but neither is it good. However, if you are Christian, it's a pity to ignore the history.
Hallowe'en is the start, the eve, of the ancient Christian (Catholic) festival of All Saints Day. Because it's catholic, puritan protestants disliked it and damned it as evil, pagan, satanic and many evangelical Christians in the USA have inherited this idea - which description also lead to the idea that it is a pagan festival.
If you remember All Saint's Day - a time to remember all holy people who went before you - the origin of the festival and of many of the customs - then that would be a good thing.