Why would that be? Btw, who is the one true living God?

Halloween,  having a Christmas tree ... various other things are of Pagan origins -should be no offense to God but only unless maybe if there is deliberate intent to offend God .

Claiming ones god as"  the only  one true living god"  is offensive to all  other religions  .....
and the rest  of the worlds  intelligence . ;-)

As for "halloween" ;
…, or "samhain" as it's really called,  It  is a new years celebration . The word "samhain" is gaelic for "summers end " . it's true date is usually early november . it is actually the PAGAN NEW YEAR , and a large pagan holiday to ring in the new year , say goodbye to summer ,and welcome winter . 

many other cultures worldwide celebrate their day of the dead events at this time . hence the inter-mixing in with halloween .
early christians tried to join in on the celebrations , dressing up as dead saints .. hence the blood in costumes , all saints / souls day ,, and devils night and devil costumes .. when this did not work . a bishop actually took the copied pagan holiday and changed it to the same night as the pagans in an attempt to over shadow it and discredit it . even though they had no idea what it was about , and concentrated more on unrelated day of the dead customs . 
the only devil , blood , and demons in halloween is the ones christians brought into it ! and put into it .!!! 

it's new years ! 
not the "blood fest" the church made it ,,, then backed off and blamed others for .

but like every other "christian " holiday that was stolen from the pagans . 
most are left to believe the lies . and the church is fine with that .
yet  im sure it would offend their  true ( or false)  ,  god .   and they only have themselves to blame . 

 

Halloween=Candy. End of story.