The one thing I hate to see is a hacked off derailleur hanger by some fixie idjit. Make it a fixie, fine, but don't handicap it for future use.
Of course, this one never had one. Lots of old English lightweight frames with cheap stamped dropouts in the rear. I've got a super cool one in my shop right now with some holes in one of the seat stays (?), wondering what to do with it.
Other than that, have at it.
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If someone tells you that you have enough bicycles and you don't need any more, stop talking to them. You don't need that kind of negativity in your life.