For the Reformatives it much more open. Choice is the buzz word when it comes to Jewish practice. Personal feelings and desires decide which mitzvos are relevant or authoritative and when with preferences changing in tune with the ongoing shift of norms within the surrounding secular liberal culture.
In short, for Orthodoxy it's about commitment and for Reformativism it's about a lack of one. And here's the problem for them: how do you build a strong feeling of commitment to a philosophy based on a lack of one?
Years ago I heard a prominent Conservative speak about how he was jealous of Chasidim, of their passion and dedication to their version of Judaism. He wanted to develop the same passion in students at the JTS. He wanted to see "Conservative Chasidim". It was a joke for those of us paying attention. Agree with their belief system or not, there is no questioning the strength of attachment Chasidim feel towards Torah and worship of the Ribono shel Olam. Their fanatical level of practice is a reflection of their desire to put God into everything they do all day long. You cannot replicate that feeling within Modern Orthodoxy, let along the non-religious Jewish groups because a level of passion that strong demands a sense of duty equally as firm. One cannot be commited strongly to being non-commited.
So it's no wonder that the Reformatives find themselves drifting as Orthodoxy continues to grow in size and strength around them. Reform may claim to have 1.5 million members but if one attempts to raise a minyan, what percentage of that horde will show up? How many are dedicated to the prinicples of Reform and how many are counted because they have a paid membership in a Reform temple somewhere? Ditto for Conservatism which is fading even faster as people search for authenticity, either on the liberal or traditional sides of practice.
How can they gain strength? A movement that makes any actual Jewish practice optional can't expect to raise large numbers for a rally. No one is going to pack a stadium with a crowd shouting "We want to do whatever we want and still be considered good Jews!" Yes, there will always be candidates for their so-called rabbinic programs but how many dedicated pro-feminist and pro-gay people who also have a liking for Bible studies are there out there? And how can they connect to congregations that see a lack of connection as part of their Jewish identity?
Ultimately, the most slef-defeating bromide is this belief:
The American Jewish community as a whole cannot survive if there is no non-Orthodox movement to which American Jews can belong; in other words, survival depends on a strong Reform movementNo it doesn't. Judaism did not need Reform or Conservative for centuries just like it didn't need the Karaites to survive. The American Jewish community shrinkage in absolute numbers, its growing disconnect from Israel, its unacceptable pathetic level of general Jewish education, is entirely driven by the Reformatives who have replaced Torah values with secular liberal ethics wrapped in a rayon tallis. Reform needs Orthodoxy (we supply them with all those OTD's) but the American Jewish community does not need inauthenticity. It needs an open admission that a lack of interest in proper Judaism is not in itself a genuine form of Judaism and to stand up and create real standards that define them. Until such time, why would anyone take their crisis seriously?