I've always found this conversation fascinating.
"Replacement Theory" has been categorized as a racist trope...but what makes that interesting - is that a lot of the migrants in question subscribe to the ideological framework that lays that out as a religious/political prescription.
When the leader of the Muslim Brotherhood (and other leaders) have used the phrase "Ballots are the new Bullets" (or something similar), and the religious texts actually outline the process of moving to new lands and outbreeding the people who already live there as a means of accumulating power from within the system, it's odd that pointing out "this is what their own ideology says they should do, and we don't want them doing that here" gets labelled as a trope.
The Arabic word (and Islamic concept of)
hijra means "migration" or "emigration," and it refers specifically to Prophet Muhammad's migration from Mecca to Medina in 622 CE, which marks start of the Islamic calendar.
The Medina migration was a political turning point. Muhammad's emigration marked the beginning of Islamic political expansion, where preaching tactics were replaced by political tactics, and the Hijra became a model that the Islamic calendar itself commemorates.
And current Islamic leaders have certainly tapped into that doctrine and flat out said they're looking for some demographic replacement.
If this were any other religious group (domestically) doing this, people wouldn't see it as controversial to call it out.
For example, if there was some die-hard Christian preacher from Texas saying "we need a bunch of conservatives to move to San Fran, have a bunch of babies, and that way we can outvote the libs and turn it into a red city a few years down the road", and then there was an influx 450k conservative Christian people all moving to San Fran in a 5 year time window (and even flipping some surrounding suburbs from blue to red), nobody would be labelling a critique of that as "anti-Christian bigotry".
If Islam was predominately a white religion, progressives wouldn't be using the kid gloves.
Every "infraction against progressiveness" that evangelical Christianity has regarding women & LGBTQ & free-thinkers, Islam has 10-fold. Yet, they'll still get agitated about an abortion clinic arson case from 2007 or a person wearing a "there are only two genders" shirt, but when you point out "hey, there's a group of people moving in, in large numbers, that make Ted Cruz look like a radical feminist, maybe we ought to reign that in a bit", it's a "whoa, whoa, how dare you say that you Islamaphobic jerk!"