No, I don't believe for one second that it's "cool" to hate TNA. The way I see it, people are free to like, or hate, whatever they so choose, as long as there's some logic or reason to their thinking.
Any hatred directed at TNA is of their own doing. They have taken what was once a plausible alternative to WWE, a different and exciting brand of wrestling which was total non-stop ACTION, something which claimed to be everything that WWE was not, and have made it an unwatchable joke. Their highly touted knockout division has gone into the toilet and is now inferior to the divas in every way, shape, and form. The X-Division has gone from their crown jewel to a disorganized clusterf**k of confusion and WWE rejects. Rather than becoming an alternative to the WWE, TNA has become a diluted version of it, with action in some ways similar to the WWE, minus the production value, the money, the storylines, the talent, the exposure, or the interest. Rather than increasing their fan base and challenging the WWE, they have gone in reverse and actually made WWE better, rather than themselves. It will take the rest of the year, as a best-case scenario, just to get back to where they were in the ratings and to win back their alienated fanbase.
The reason I find it easy to hate TNA is not because it's cool, but rather, because they brought it all on themselves. Instead of just going about their business and making a gradual progressive run at WWE, they shoot their mouths off constantly, making it easy to expresss negativity toward them when they fall on their faces as they do over and over again. Whether it be Hogan claiming they'll get a 3.0 rating on Jan 04 (I guess simply because Saint hogan has arrived), or Ric Flair claiming TNA will be equal to WWE in 6 months, or Bischoff or Carter claiming they're taking the wars to Monday nights, only to retreat with their tails between their legs when they couldn't follow through, or lastly, to the stream of disgruntled former WWE guys (Angle, Hardy, RVD, Kennedy) who cannot open their mouths without taking pot shots at Vince and the WWE, all of these things make it very easy to be negative toward TNA.
I would respectfully suggest the reverse to be true. I think it has become "cool" for the anti-establishment guys to espouse TNA and be critical of the WWE. It seems to be in vogue for the TNA smarks to continually praise TNA and express constant negativity toward WWE, whereas in reality, it's hard to imagine that anyone could really and truly feel this way. It has become cool to say: Cena only knows 5 moves, or HHH is only where he is because he married the boss's daughter, or WWE has become stale, etc., Whereas in reality, WWE is so far ahead of TNA it's actually laughable. And I truly believe this will never ever change.
I choose to watch what I watch, like what I like, or hate what I hate, not because it's cool, but because I will make my own decisions based upon the respective products as I see them. I will not watch TNA because some TNA smark tells me I have to, that I'm not a "true wrestling fan" if I don't, or that I have to because somehow I'm compelled to to make WWE better. I let the products speak for themselves. And they're speaking loud and clear these days. WWE all the way. By a mile.