You may be interested to read the National Science Teachers Assocation's position statement on the Responsible Use of Live Animals and Dissection in the Science Classroom:
(broken link removed)
There is nothing in the statement saying that students should be forced to dissect; rather, they make a point that there should be pedagogically sound reasons for choosing dissection as a teaching tool, and that teachers should be sensitive to student objections and needs, including finding alternate and meaningful activities.
I teach undergraduate non-majors biology at a community college, and the only dissection we have in all three terms is the grasshopper -- and that is optional. Most of the time when non-majors students dissect, as they did in the university where I taught for a while, they do a quick "cut, look, throw away," which doesn't teach them a whole lot. There are better ways to teach anatomy, even comparative anatomy, than handing every student a dead animal and making them carve into it.
In my opinion, routine dissection is inappropriate for non-majors and for regular high school biology. Teachers who still use it are usually following the lab curriculum that comes with the textbook. Usually the lab books have people dissecting pigs when studying mammals, dissecting frogs when studying amphibians, etc. I prefer to use an ecological focus and discuss what the animals are doing in their evironment and how they are adapted to their ecological niches. At most I may use specimens or a limited number of dissected specimens to demonstrate comparative anatomy, but photographs, diagrams, and online resources often get the point across much better.
It's ok, it happens.
