The point is that demands, by either party, are not the best. My guess is that in many cases, we (crossdressers) don't do a very good job of explaining how all this sits for us. Note that this is NOT attempting to explain the WHY behind what we do. It is possible that the shame and guilt that we sometimes feel, to say nothing of denial, may prevent us from being candid about this activity that we do. Fear of potential outcomes can also drive us to be less than candid.
The other point is that, transgender issues aside, we're talking about human relationships. Often we have some very rigid ideas around how those relationships should be structured and where the lines are. It's obvious that learning your partner is into an activity that can have far-reaching consequences for the lives of all concerned is often an upsetting experience. But, acceptance shouldn't be automatic; and neither should rejection.
I think the statement "I married a man, not a woman." is a bit lame. If you broaden that out, did any of us set out to marry a cancer patient, a schizophrenic, a stroke victim, etc.? Most often, no. If those things happen usually we try to deal with them as best we can. For a few, those kinds of circumstances can overwhelm a relationship. But, in part, a major difference is that we can see the result of having those medical issues. While you can see the external veneer the we crossdressers put forth, much of the actual shift happens internally. That is probably very disconcerting for our partners.