That’s a reasonable point. The fact that he shared intelligence with Russia is not necessarily the problem. It’s not the first time we shared intelligence with Russia. The problem is this specific intelligence.
The material Trump shared was provided by a foreign ally on the condition that it not be shared with another country. Trump broke that agreement. The ally may not be willing to trust the US with similar intelligence in the future. Maybe Russia shares it with Syria or Iran, its allies in the region and it finds its way to ISIS, they might be able to hunt down the mole and plug the leak. Maybe none of that will happen, but steps should have been taken to mitigate the risk that it would. That didn’t happen.
It appears that Trump shared this material impulsively without considering the ramifications. There’s no indication that Trump had planned to share this before he got into the room. If the information would prevent an attack on a Russian airliner, certainly sharing it with Russia might be prudent. If it had been done in consultation with the ally who provided the information in a way that protects the source of the information, that would have been fine.
At the end of the day it wasn’t our intelligence to share. But, it was ultimately Trump’s call. The buck stops with him. But so does the blame for any fallout. If we lose access to this reporting steam as a result and an airliner is blown up that could have been prevented, the fallout will be grave indeed.