Au contraire, as Del Boy would say, the benefits of using a semi-auto for pigeon shooting outweigh the disadvantages.
Number one, a decent model is relatively cheap.
Number two, recoil is greatly reduced, a significant consideration if you are firing a large number of shots in a day – and you have the extra third cartridge if you need it.
Devotees say they are easier and quicker to reload in the confines of a pigeon hide too.
The downside is they are a bit cumbersome in their handling and are prone to malfunction if not scrupulously cleaned after every session.
Also, some models refuse to cycle properly with loads lighter than 28 grams.