JF2: It’s true that many or most people nowadays who call themselves Conservative or Reform do not necessarily believe in (or know) the ideology of those movements, and therefore the things I wrote might not apply to them. I was thinking of mentioning that, but didn’t since: a) my post was long enough b) it wasn’t really necessary since it doesn’t negate the point that I was making. I was talking about people who do believe in the conservative or reform ideologies.
In any event, the Rabbis themselves do believe in the ideology and when people identify with the movements, they are strengthening movements that are kefira and that is a serious problem, even if it is inadvertant.
If they want to keep some Mitzvos, that is great, and it is not necessary to belong to a conservative or reform synagogue in order to do so. There are plenty of people who keep some of the Mitzvos w/o identifying with conservative or reform.
In Eretz Yisrael, the conservative and reform movements are, Boruch Hashem, almost non-existent, and your average Secular Israeli Jew keeps many more Mitzvos than the average conservative or reform Jew in the US. And most importantly, they keep THE MOST IMPORTANT Mitzvah which is not being an apikorus. Better not to keep the Mitzvos than to deny the truth of any Mitzvah, which renders someone an apikorus, as Joseph pointed out. And the average Secular Jews keep many Mitzvos than the average American Jew.