First, let's talk about the Sentai haters. What good reason is there to hate Sentai? Well, for a Power Rangers fan who finds themselves amongst a crowd of Sentai fans... it's not fun at all. No matter what anyone thinks, Sentai truly is the more better made franchise of the two, no question about it. It does not matter what your opinion is, Sentai is much better. That's a fact. And as a PR fan, putting up with Sentai is a nightmare. Of course, every PR season has something good to it. But compared to Sentai, only like two of PR's seasons can really compare to it. Many Sentai purists are so disgusted with PR's inferior quality, that's it no wonder that this stirred up hate from the PR fans. It's also true that a good number of Sentai fans tend to fail to see any of the good quality from PR, and thus, just choose to bandwagon in on Sentai, which also angers PR fans.
Another reason why PR purists can hate Sentai, is cause it crushed their nostalgia. Many of them felt like their childhood was just a lie. Though honestly, this could just be a bad reaction from some people.
Some PR purists go so far to even compare Dairanger (one of the most well made sentai) to MMPR season 2 (a season that's controversial to some). This also angers Sentai fans, as many agree that Dairanger should never be compared to a show like MMPR season 2. And thus, both sides back lash over and over again.
Next, let's talk about the PR Haters. What sort of good reason is there to hate Power Rangers? Well, many Sentai fans absolutely despise the fact that Power Rangers affected the tokusatsu genre in the worst way possible. And making the genre look very kiddy to the public. Thus, many toku fans blame Power Rangers for the reason why no toku will ever be properly released in the States.
All toku (even including Ultraman), especially Sentai, keep being called "kiddy Power Rangers" by people. As you can see, PR truly has affected the image of toku. And many toku fans have to put up with it all the time. Thus, making this another understandable source for the PR hate. And it makes things worse for them when it's a fact that PR is THE most popular toku worldwide, while the rest of toku pretty much only exists in just Japan. In other countries that used to air toku, it all got replaced with just PR.
I'm sure I missed some stuff here and there. But overall, there are many fans that have justifiable reasons for why they hate the opposing shows. And many of these fans just end up acting like jerks because of this. So what can they do to fix this? Well, I'd say for starters, to just forgive the opposing shows and just move on.
The PR and Sentai hate started when Sentai was discovered by many, starting with Dekaranger. And it got worse when PR entered it's four year Dork Age with the Bruce Kalish seasons. And things continued to be bad when Sentai now entered it's Dork Age with the Jun Hikasa seasons (except Shinkenger), which it is currently in the middle of right now. Both franchises will have it's bad seasons. There's really NO NEED to bash an entire franchise just for a few bad seasons! Because you can't just forget about any of the cool stuff that both franchises have done.
I understand that fans of both franchises have had long histories (including myself). But like I said up above, forgive the opposing franchises, and move on. And try to be as positive as you can. Cause hate is just not fun at all. So it's best not to cling on to it (I learned this from my own experience). Remember. PR is coming back from cancellation, under the hands of Saban! And Sentai is in a mess right now, but we know it can do better! And the anniversary is next year! If PR can get out of a horrible Dork Age and follow it up with something as awesome as RPM, then so can Sentai! So forgive the opposing franchises, move on, and root for the success of both shows! :D
PS: Sorry if I sounded overdramatic. But I didn't know how else to phrase what I was trying to say. xD
And I hope what I said in this post made sense. :)