What are the consequences of withdrawing an abstract from a conference?
First, I should mention that the "no paper, no podium" (and vice versa) only applies to conferences where proceedings are published. For many conferences, this is not the case—including many conferences in physics, chemistry, engineering, and applied mathematics that I regularly attend.

In general, if you have to withdraw a paper because of whatever reason—visa issues, experiments not working, or kidnapped by aliens (etc.)—it will not have that much impact on your career. The effect will increase, however, the more papers you withdraw, and the more trouble that you cause the conference organizers as a result. If you let them know well in advance that you're not going to be there, they can try to organize some sort of replacement for you, which, although suboptimal, is better than having a "hole" in the schedule. On the other hand, if you wait until the morning of your talk to withdraw your talk, you will definitely tick off the organizers, which may have an effect on your ability to present in the future (at least at that conference, or others the organizers work on later).