Who did the original Hebrew Christians "replace"? Were they not simply remaining faithful to God by accepting their prophesied Messiah at the time of their visitation? Obviously, the term "replacement theology" would have sounded ridiculous to them, as it does to any honest person today.
The problem is when the Gentile Christians forgot that it was they--not the Jews--who had been graciously adopted into a pre-existing family and began persecuting your adopted brothers for continuing to keep the household rules that had been established 1500 years before your ancestors knew there was only One God. It wasn't enough that you were (arguably, there are some debates to be had here but I won't go into them today) exempted from certain commandments--you jealously persecuted those who continued to keep them, calling them heretics. At that time, the "Hebrew Christians," were forced to either assimilate into what had become a Gentile culture in the churches or were forced out.
The moment Gentile Christians not only forced the Torah-observant Jewish believers from their midst but also declared yourselves to be the "true Israel," the term "replacement theology" became an accurate descriptor. You who call Judaizing Gentiles anathema proudly boast of Gentilizing Jews.
Dispensationalists may not fully understand their adopted status, but at least they acknowledge that the Father who adopted them still loves and will keep His promises to His firstborn son.
Shalom.