Since watching them, something about the two episodes has been bothering me. Finally this morning I realized what it was: the writer's desire to send a message with their story kept poking up and getting in the way of what is an otherwise pretty decent story. And, when this reminds me of another similar incident where a play I saw years ago at The Victory Garden theater (in Chicago) - something like Spinning Into the Blue - was similarly distracted by the playwrights message, I realized there was another minor factor, the fact that the message in both cases could have been changed, or just gone away, with a few minor changes in the script.
In the case of "Blood and Fire" I actually missed the author's message until I did some research - in this case looked at the episode guide on Wikipedia, where it mentioned that these episodes had been originally proposed for Star Trek: The Next Generation, but were rejected due to "its controversial storyline dealing with homosexuality and AIDS." But, with very minor edits - specifically changing a few personal pronouns from "him" to "her" (and similar) and one line from "husband" to "wife," and not even changing the name of the character Alex Freeman, nothing else about the story would have changed. So what was intended as a message just became a bit too explicit of a distraction (and other than the fact that two men were involved there was nothing on camera that wasn't on camera in circa 1968 Star Trek).
The play had a similar flaw. The playwright had written what I'm sure she thought was a powerful message in support of the need for safe and legal abortion, but again with just a couple of changes in the play - and in this case a couple of lines near the end - the same action would have become an equally good story about how abortion can ruin the life of the women who chose, or in some cases are practically forced, to go through it.
So, I think what bothered me in both cases wasn't a bad story, nor necessarily a bit of message buried in the story, but an author thinking that they are burying the message when they are in fact putting up big, distracting, flags that say "here is my message!" and not even noticing that their message ins't all that much there. I'm not sure that the fact that I tend to lean away from the most radical forms of either of these messages (but do not necessarily support the most extreme other side either) did not cause as much a problem as the way in which the message jarred the stories.
Back to "Blood and Fire," the wikipedia entry mentions "AIDS" as part of the story. But, perhaps with a 2010 filter, rather than a mid-1990's filter, in place I see the Regalian Blood Worm/Plasmasite problem as more akin to Ebola or some other fairly easily transmittable and fairly rapidly deadly disease than to AIDS which is well known to be pretty hard to spread (or at least easy to not spread) and one that is proving almost survivable. Perhaps the only relationship with AIDS (and again this would make more sense in the 1980's and 1990's when AIDS was still seen as primarily a disease in the homosexual community - instead of a worldwide pandemic centered in poor African countries as it is seen now) was the aspect of a copule of characters choosing suicide rather than suffering through the disease to the end. But, again there are plenty of similar actions in anyone suffering from a dread disease.
Now, just as a counter, having a message doesn't necessarily ruin an already shaky story. I'm pretty sure I'd have found The DiVinci Code pretty poor even without the author trying to tell me that almost everything my faith and religion teaches is wrong; and I would have realized that The Left Behind series was a poor story interrupted by unnecessary sermons even if I weren't intrigued with using it as a way to understand one view of eschatological scripture (and, for the record, I'm not convinced it is the correct view and am convinced that it is not that important of an issue in any case).