There is a saying that if you tell a lie often enough people will begin to regard it as truth. So yes, of course there is a point to arguing with “the haters” on social media. You have to. You don’t need to be rude or vulgar in your rebuttals but you do have a responsibility to not just sit silently by and take it. Don’t let the lies get enough traction to start becoming truth to the weak minded. Speak up!!
As to your side note, hard core anti Semites make no differentiation between observant and secular Jews. To them a Jew is a Jew is a Jew. They would need six active and firing brains cells, which they sadly lack, to make the differentiation. A secular Jew is like a secular anything else, they want to do whatever they want, whenever they want, without having to answer for their behavior to a governing deity. I am more saddened by secular Jews wanting to separate themselves and stand apart from observant Jews. Like they’re embarrassed or something and don’t wish to be associated with the observant. Practicing or not, secular or observant, they should be proud to call themselves a Jew.