They're not being forced to do anything. The patent office took away the protection of their trademark because it's a slur. The first amendment protects your freedom to use a slur, not to make a profit from it.
Semantics...That's like saying the Federal government did not institute a nationwide minimal drinking age law of 21. The Department of Transportation merely informed the state legislatures that they were going to lose out on highway repair funding if they didn't. Congress, by way of the patent office, is not technically "forcing" the Washington Redskin Football Club to change their name, but they unlocked the door, turned off the alarm, and allowed newspapers to accumulate on the front porch.
This is not a first amendment issue but since you brought it up, you may be interested in
this.
I guess at the root of the argument for me is to determine if "Redskin" is really a slur. I am not about to take Merriam-Webster's word for it either. These are the same people who felt the need to define
OMG, mankini, bromance, muggle, and riffage (what? Did it really get too hard to look up guitar and riff separately), among other plays on actual words.
I guess, for me personally, I don't consider it a slur because 1) it is far removed from any other potential meaning (for me) and 2) more importantly, there is reasonable doubt in the populous. According to a sample of 1 (which is as scientific as what the Patent Office sites), I have not really heard the term Redskins outside the context of the Football team (it's use in
Thunder Heart as a play of words notwithstanding, which I thought was kind of clever.).
Now that said, if they choose to change the name, then fine. I don't think it should be government enabled, especially by members of the current (most historically inefficient) session of Congress.