This isn't a question really if Global should or shouldn't. Broadcasters wouldn't normally be deciding who or who can't advertise on their station. As long as the product or company is legal, and nothing hateful or anything libelious or in bad taste is promoted any broadcaster wouldn't likely turn down the advertising. The station should point out to the advertiser the risks involved, and the fact the ad could give them publicity that they don't necessarily want, or even hurt their product.
A mother and daughter company has been advertising on CP24 about moving your business to the US. The ad starts off with something like "are you tired of paying high Canadian taxes.." The ad shows the two in the nice warm weather on the beach sipping a cool beverage and commenting how easy it is to move. To me this ad is inappropriate at this time, but was CP24 or Bell wrong in running it? Not really. I am sure the station and the company involved has heard an earful from people both upset with the commercial but they have also likely heard from a few considering a move.