What about the koranic verse where Allah forbid Rasoolallah from going to a munafiq masjid?
i cannot remember the exact verse as i’m not a hafiz or mulla, but i know it exhists becuase i’ve come across it before. Perhaps another brother can eleborate it for you. Now how can we accept that your masjid is justified if Allah forbade his rasool from attending a munafiq gathering?
As a sunni i cannot go where my nabi was himself forbiden to do so (aka haraam)
Hope this isn’t off topic as well?
As for why we pick on Ahmadies, well put it simply even if you don’t harm me in any way, by slandering my prophet you’ve commitied a crime tantamount to a declaration of war. I’m not just saying that it’s in the koran as well! So it’s my religous duty to oppose Ahmedies just like Jihad is a religous duty.
Now if you tell me you do not accept the koran then please tell me why you Ahmedies still call yourselves Muslim???
Furthermore as my Pir Murshid put it, it’s not the actions of a person that define his faith (i.e Ammaal) it is the belief within, (i.e. Aqeeda) if your belief is flawed then no matter how pious you behave you are not true Muslim!
So coming back to the point, if Ahmedies come out and say that they are an offshoot cult (which they are) and follow a misguided man who was not a Muslim himself (Mirza) then i can say with confidence that they will not be so persecuted.
However Ahmedies stubbornly cling to offensive beliefs, did you know Mirza wrote more lies than anyone since Judas. He not only calimed to be a (false) prophet, he also called himself Imam Mehdi, the Messiah, Jesus… and if he hadn’t insulted enough people with those comments he went on to claim Mughal titular-ship (OK maybe he was a Mughal nobleman 
) but he also claimed to be Miriam/Mariam aka Mary mother of Jesus!
Now tell me you don’t believe all that do you? If Ahmedies stubbornly cling to this cult leaders dellirious beliefs and respect his written words then can you blame Muslims and others for out and out hatred towards the Ahmediyah?
Now seriously i’m enjoying this debate, sorry for any personal attacks i may have launched. I’m from a millitralistic background so i might not be as “civilised” as you but thats no reason to ignore me. Infact my fanatical viewpoints might help you understand why Ahmedies get so much stick?