Doesn't this statement reflect an anti-semitic attitude on the part of the writer? We shouldn't forget that such a view about the Jews was commonplace among the pagans
Just to clarify: there's a difference between being anti-semitic and anti-Jewish. Anti-Jewish basically means you don't believe in the religion or practices of the Jews, which is what is under question here. Being anti-Semitic basically means a hatred of all things Jewish: their religion, culture, ancestory and nationality. Early Christians were more anti-Jewish because if a Jew converted to Christianity, they were welcomed with opened arms, no questions asked. That would never happen with a group who is anti-Semitic because to them, there is nothing redeemable in a Jew. Hitler and his henchmen were all anti-Semitic.
With that said, there is some debate with scholars (no, not the 'WT celebrated scholars' but genuine ones with a PhD after their names) as to whether Paul actually wrote this passage in 1 Thess. because Paul, in his writings and as a former Pharisee himself, did not express hatred towards his fellow Jews. Matthew 27: 24-25 makes it appear as though Pontius Pilate actually tried to save Jesus' life, but caved to pressure from the apparent blood-hungry crowd of Jews who were demanding his head on a platter so to speak. Pilate famously 'washes his hands' of the affair and the rest is history.
However, to anyone who's actually studied this time frame in history, I sincerely doubt Jesus' death panned out exactly the way it is described in the New Testament. First of all, there is no historical evidence of the Romans having a "tradition" of releasing a prisoner to the Jews. Secondly, Pilate was no wimp and if there was in fact a crowd of Jews who were starting to get out of control, he would have dealt with it with swift and brutal violence. And thirdly, Jesus was not a threat to the average Jew. He was, however, a threat to the Jewish leaders as well as to the Roman occupation. It is doubtful that every single Jewish leader wanted him dead and under Jewish law, Jesus could have been convicted on as little as "two witnesses".
My own opinion on it is that after Jesus' execution, some of the newly formed group of Christians probably grew increasingly bitter at their fellow Jews for refusing to accept Jesus as the Messiah and in the earliest writings, the blame shifted away from Rome and some of the Pharisees and onto the average Jew instead. Another possibility is that the writers might have been hoping to gain a measure of freedom under the Roman occupation and if they blamed the Jews for killing the King of the Jews instead of the Roman governor, it might work in their favor. (of course, it didn't, but that's another story).
The New Testament gives the idea that no more than 20 or 30 years after Jesus' death, that tension between Jews and Christians was so bad it could be cut with a knife, but this isn't really so. The newly formed Christians continued to preach in the Synogogues up until the destruction in 70CE. The split between the two groups did not happen all at once, but it happened gradually over then next 3 centuries. While some put the final parting of the way between Jews and Christians at the Council of Nicea in 325 CE, others put it as early as 70 CE.
What's so tragic though, about these passages in the NT, is that they were used for centuries as justification for Pogroms against the Jews. To this day I'm amazed at how many people are ignorant of the fact that Jesus himself was a Jew, not a Christian.