If a tackle is hurtful, is it considered lawful or not? If one gets hurt during a tackle, does it mean?

I saw the incident with Trengove and I believe it's a bloody disgrace. The AFL these days seems to be taking away the fun out of the sport we all love to watch. It's like you can't do anything these days. You take a mark and you get penalized. It's just all a load of bull. The tackle wasn't even dangerous when I looked at it.