Oh the militant supporter of (insert your choice). Their passion/obsession/cause/personal belief system overrides everyone else's comfort and polite society's expectations. Go over to the home of your husband's co-worker and make sure everyone there know your views on (insert your choice). Refuse to discuss anything but (insert your choice). Make sure to cut off the host/hostess/other guests' opinions/comments/random thoughts on (insert your choice) because they obviously don't have the expertise/same opinion/a freaking clue on said subject as the militant supporter does. Be sure to do/talk about/expound upon/demonstrate/show pictures of (insert your choice) multiple times in their presence no matter how uncomfortable the people around you may be with it.
Add to it the expectation that your hosts are comfortable with a diapered baby sitting on the same table surface where everyone is eating and then changing the said diaper on carpet, without cover because you don't believe in basic sanitation when it comes to such things.
Sounds like the guest from the depths of e-hell to me.
When the wife decided to change baby on the carpet, that is when safety trumps etiquette for me. The potential mess/contamination that this action could cause can be a health hazard and a cleaning nightmare if the diaper is full. I would have stopped her and said let me get a towel for that. If she continued to refuse, I would have become quite vocal in that I didn't want baby (biological fluid/matter) on my carpeting.
Of course the long-term answer would be to never invite them to your home again. If your husband wants to socialize with his co-worker, a guy's night out or an afternoon golf game is the answer. If said couple invited you and your husband to their home for dinner, I would refuse the invitation. If they pressed on the reason for the refusal, I would actually be blunt in that I like to discuss things other than breastfeeding when I socialize.
(And for the record, I fully support a mother's right to breastfeed. I just think it can be done in a way that is comfortable for everyone, including baby and mother, without offending everyone within a mile of it.)