It is not common, and I'm surprised by the conclusion that those players are simply toxic/trolling. In my ranked game experience, 90% of time teammates do want to win. I understand your frustration of intended pick getting banned, but there could be a reason why your planned pick gets banned frequently.
Intended picks serve as a way to communicate, and there are people who truly feel the pain to have certain champion on their team, or played by certain players. One time I checked my teammates' status and the top laner decided to go Garen with 14% winrate with 30+ games. I dodged, but I can understand those who decided to ban Garen for a win.
Meanwhile, I believe players who ban teammates' intended picks are not trolling. They simply don't want that champion on their team. They want to secure a win and/or have good game experience. It is not pleasant to have a support planning to play Tryndamere.
Respect is mutual: when I expect my teammates to respect me by showing my intended pick, I am also respecting their decisions. Have you tried to communicate with them when showing an intended pick which a lot of players won't like?
With a more positive attitude you will (hopefully) move onto a rank where even the most exotic picks won't surprise your teammates.
If moving around the rank ladder was not an option, I would suggest you not show your intended pick and see if anything changes. After all, most players play ranked games seriously--starting form a decent rank.