I do not deny that climate has changed in the past. I do have a disagreement with the idea that it has "always changed", because I don't know what that means and I don't think people have the evidence to support this idea once it's defined.
For example, we're concerned about the time change over a several hundred year period, from the industrial revolution to the next century or two. When people say that the climate has "always changed", for their comment to be relevant, it should always have changed over similar time periods to the one we're considering. My first problem is that they don't define what they're talking about. I guess they mean that the global mean temperature has always changed over such time periods, and the changes that have occurred are similar in magnitude (~1K) to what we've seen. If they don't mean that, then why bring it up?
If they do mean that, I don't think they have any evidence whatsoever to support their claim. Think about it, if we round up and take 5 billion years for the age of the Earth, and use 100 years as our relevant time period, then there have been 50 million such time periods over the history of the Earth. We have reasonably good instrumental data for perhaps two of those. Over Earth's recent history, we have some imputed temperatures from proxy records, but those are bound to have bigger error bars on them than the instrumental records. Go back a billion years, and all bets are off, we simply have no time resolution whatsoever on the order of 100 years, much less the data that could resolve a 1 K change over all those time periods. The global mean temperature could have changed 0.5K, 2K or 5K over a one hundred year period, and it's doubtful that we would know. Perhaps we could narrow a 5K change to a few thousand years, but the idea that we could tell a 1 K change versus a 0.1 K change over a particular century back then is ludicrous.
So when people say "The climate has always changed" we should see that for what it is--an unsupported truism based more on faith than on science. They say it to as a way of dismissing the very real climate change that is happening today and that humans are causing--change that we can see and measure--instead of their imagined climate change of the unspecified, unmeasured past.