Technically, you are doing nothing wrong if you put up decorative lighting (whether around Christmas or not). This, especially if you are putting icicle lights (they are winter theme), clear lights (again, winter theme), or you are using them for other purposes. Lights can be used to outline a property, for security, or to spread light in places where it's dark and difficult to light properly. And, there is plenty of evidence that color therapy does some good (which Christmas lights can be used for).
However, the hounders are not looking at technical things when it's in your favor. They claim you are stumbling others. Or, they think you are displaying "brazen conduct", especially if they tell you to pull them down and throw them away and you don't. Plus, they take time and money that "should be donated to the Worldwide Pedophile Defense Fund". Each strand of Christmas lights, whether you use them for Christmas or to showcase your plants, costs between $2-5 (incandescent) or $8-30 (LED; some colors are more expensive than others).