I live in Cornwall, and have done all of my life, I was born here. I also work in hospitality. (Full disclaimer. I am not claiming anything I say is only relevant to Cornwall.)
It goes without saying that I wouldn't have an income without tourism. I live in a lovely area and I like being able to share that with others. I don't tire of making acquaintance with lovely visitors who appreciate and respect the people who live and work here. That's 90% of tourists by the way!!
Overtourism as PP mentioned is different and I encourage everyone on the thread to consider this as a genuine problem rather than locals needlessly complaining. While I am extremely grateful that tourism could open up last summer (could we have survived without it?), it brought problems too. Queues of traffic, making it insanely difficult for anyone to go about their daily lives. Every establishment was ridiculously understaffed (in my experience); there just were not enough people available to work, and workers (including myself) were nearing burnout.
I love where I live, I love tourism, I need an income and I enjoy sharing my local area with others. I like to go on holiday myself, and this would make me a massive hypocrite if I hated tourists! But the attitudes of visitors makes a humongous difference. Like I said, 90% of visitors are lovely. But a respect for the people here is a necessity. It is not our fault that you queued for half an hour to get here, or that you need to make reservations in advance instead of walking in, that you wait a little while longer for your meal. Most people know this! But there are always (ESPECIALLY last summer) people that treat the locals with a huge disrespect and really do forget that people live and work here. I think that is where the 'hostility' comes from and over time, it brings us down.
Please no one be put off visiting Cornwall due to a perception of angry locals. We can deal with the queues and the jam packed ness (as it means we get paid!) as long as we're treated like human beings! Which most tourists do.
((Perspective of a hospitality worker and I appreciate not every Cornish local will feel the same.))
In regards to second home owners I think the general consensus has been covered. Not just a Cornish issue as others have said.