1. OK.
2. I am assuming we = humans. No one knows what intelligence is. Scientists are still arguing about what it means. I am going to assume that by intelligence you mean whatever an IQ test measures. You are said to be more intelligent than me if your IQ score is higher than mine. Now, put a 5 year old chimp and a 5 year old child to do an IQ test and let's see how different their scores are. My bet is that there will be a difference but what do we conclude from that? Brain-damaged individuals will also score low. Fact is: some life forms (both human and non-human) will score high and other life forms (both human and non-human) low. Should we then give rights on the basis on IQ?
3. Are we? We certainly do have teeth and can process meat but it does not follow that we were designed for x. Eating meat is an evolutionary trait that we have. But I would not say that we are designed for x. Let me give you an example. Rape and infanticide can be found in many species and one could think that it is an evolutionary advantage to do these things but I would not say that we are designed for that. And even if we were, I would not say that rape/eating-meat/infanticide is okay just because it gave an evolutionary edge to my ancestors. This was just to put your "we were designed for x. We've been doing it for hundreds of thousands of years" in a wider context.
4. "There isn't a valid reason why it should be forbidden." That depends on what mean by a valid reason. Similarly, many people would say that "There isn't a valid reason why x should be forbidden." where x could be something of benefit to someone (for example: slavery for slavers).
5. "Some people exercise their right to choose" I would not call it right. I would call it power. It does not have the metaphysical connotations of the word "right" and is more physicalist. "and fair enough to them but I strongly disagree with them." Why?
6. Assuming there is no negative effect in the safety/taste of the meat that comes out, I am curious as to why do you so care so much for their suffering if you are going to kill them for your pleasure?
Sorry if I wrote too much.