Nonsense Hope. It's not technically impossible at all.
People can convert to Judaism if they want, I've looked into it.
I've looked into it as well, Rose and been told by several rabbis that one can't be a full Jew without Jewish blood somewhere on one's mother's maternal side.
Furthermore, conversion is to a specific denomination of Judaism, as opposed to Judaism as a whole, and often one's conversion under the requirements of a given demonination will not be accepted by other denominations. Then, there are certain denominations who won't accept any conversions. I have spoken to Hasidic Jews who say that it is impossible to convert to that form of Judaism (though I have also spoken to what you might call 'lapsed' Hasidic Jews who say one can).
A convert is supposed to be treated equally to any born Jew.
The problem is that further down the line, genealogies struggle to get past the 'Gentile' convert, thus making proof that one is a Jew difficult.
Regarding Ruth, she was not a convert. She was married to a Jew and chose to accompany Naomi back to Israel when Naomi's two sons died. If you look at the genealogy of Jesus in Matthew, you will find four occasions when someone is referred to as being the son of X - Judah, Salmon, Boaz and David BY Tamar, Rahab, Ruth and 'the wife of Uriah' respectively. Clearly, there is something different about these 4 women - they were all non-Jews.