IMHO: Theodor Herzl had his heart in the right place. Namely. The resurrection of Jewish national pride in their own homeland. But, since he was born and educated into an assimilated Jewish family he had no concept of a lifestyle that is in accordance with Torah and Halacha. To him Christianity was just as good as Judaism as a national religion for the Jews. His ultimate goal was of obtaining a national homeland for the Jewish people. And if the Jews would have to accept Christianity along the way didn’t stop him from attaining his goal.
It is a well documented fact that he (Herzl) was inspired to work towards achieving a Jewish homeland at the outcome of the Dreyfus trial. When Alfred Dreyfus, a high ranking officer in the French Army was found guilty of espionage and stripped of his rank, Theodor Herzl realized that the Jews will never achieve equality in the lands of Europe, where they tried so desperately to assimilate and be like the rest of the population.