What are the cons of extraction of last upper molar compared with root canal and crowning crown?

Tooth. Is the tooth in function, meaning does it have a tooth on the bottom to bite against? If so, does your dentist think you will get more than 5 yrs out of RCT and Crown, if not may be better to extract and place an implant, especially as you are a young guy..
Risk losing more . Generally, when a molar tooth is removed, the risk of losing adjacent and functioning teeth increase. Teeth need each other to prevent them from shifting and drifting. Once that occurs, bone loss accelerates and increased mobility increases the probability of further tooth loss. Much better choice to save the molar with root canal and crown.
Tooth migration. The root canal and crown are the way to go! losing the molar will long term cause the lower molar that opposes the extracted tooth to extrude or over-erupt, causing your bite to be off. Also, always save a good tooth so that your dentition remains complete for proper chewing!
Tooth extraction. will remove a tooth from your mouth leaving a gap that could reduce the functionality of your bite and can impair the cosmetic appearance of your face. Alsocomplications may occur during or after tooth extraction is done.